Method and device for video decoding, and method and device for video encoding

ABSTRACT

Provided are a video decoding method and apparatus which, during video encoding and decoding processes, determine whether a current block is in contact with an upper boundary of a largest coding unit including the current block, when it is determined that the current block is in contact with the upper boundary of the largest coding unit, determine an upper reference line of the current block as one reference line, when it is determined that the current block is not in contact with the upper boundary of the largest coding unit, determine the upper reference line of the current block based on N reference lines, and use the determined upper reference line.

TECHNICAL FIELD

The disclosure relates to a video decoding method and a video decodingapparatus, and more particularly, to a video encoding method andapparatus and a video decoding method and apparatus, in which, when atleast one reference line is used, in a case where a current block is incontact with an upper boundary of a largest coding unit including thecurrent block, an upper reference line is determined and used as onereference line.

BACKGROUND ART

Image data is encoded by a codec according to a preset data compressionstandard, e.g., the Moving Picture Expert Group (MPEG) standard, andthen stored in a recording medium or transmitted in the form of abitstream through a communication channel.

With the development and spread of hardware capable of reproducing andstoring high-resolution or high-definition image content, the need for acodec that effectively encodes or decodes high-resolution orhigh-definition image content has increased. Encoded image content maybe decoded and then reproduced. Recently, methods of effectivelycompressing such high-resolution or high-definition image content areused. For example, a method of randomly splitting an image to be encodedor a procedure of manipulating data has been proposed to allow an imagecompression technique to be effectively implemented.

As one of data manipulation techniques, it is common to use one or tworeference lines to perform prediction.

DESCRIPTION OF EMBODIMENTS Technical Problem

Provided are a method and an apparatus, which, during video encoding anddecoding processes, determine whether a current block is in contact withan upper boundary of a largest coding unit including the current block,when in contact with the upper boundary, determine an upper referenceline of the current block as one reference line, when not in contactwith the upper boundary, determine the upper reference line of thecurrent block based on N reference lines, and use the determined upperreference line.

Technical Solution to Problem

To solve the technical problem, a video decoding method according to thedisclosure includes: determining whether a current block is in contactwith an upper boundary of a largest coding unit including the currentblock; when it is determined that the current block is in contact withthe upper boundary of the largest coding unit, determining an upperreference line of the current block as one reference line; when it isdetermined that the current block is not in contact with the upperboundary of the largest coding unit, determining the upper referenceline of the current block based on N reference lines; and performingprediction on the current block, based on the determined upper referenceline, wherein N is a natural number.

To solve the technical problem, a video decoding apparatus according tothe disclosure includes: a memory; and at least one processor connectedto the memory, wherein the at least one processor is configured to:determine whether a current block is in contact with an upper boundaryof a largest coding unit including the current block; when it isdetermined that the current block is in contact with the upper boundaryof the largest coding unit, determine an upper reference line of thecurrent block as one reference line; when it is determined that thecurrent block is not in contact with the upper boundary of the largestcoding unit, determine the upper reference line of the current blockbased on N reference lines; and perform prediction on the current block,based on the determined upper reference line, wherein N is a naturalnumber.

To solve the technical problem, a video encoding method according to thedisclosure includes: determining whether a current block is in contactwith an upper boundary of a largest coding unit including the currentblock; when it is determined that the current block is in contact withthe upper boundary of the largest coding unit, determining an upperreference line of the current block as one reference line; when it isdetermined that the current block is not in contact with the upperboundary of the largest coding unit, determining the upper referenceline of the current block based on N reference lines; and performingprediction on the current block, wherein N is a natural number.

To solve the technical problem, a video encoding apparatus according tothe disclosure includes at least one processor connected to a memory,wherein the at least one processor is configured to: determine whether acurrent block is in contact with an upper boundary of a largest codingunit including the current block; when it is determined that the currentblock is in contact with the upper boundary of the largest coding unit,determine an upper reference line of the current block as one referenceline; when it is determined that the current block is not in contactwith the upper boundary of the largest coding unit, determine the upperreference line of the current block based on N reference lines; andperform prediction on the current block, based on the determined upperreference line, wherein N is a natural number.

Advantageous Effects of Disclosure

During video encoding and decoding processes, whether a current block isin contact with an upper boundary of a largest coding unit including thecurrent block is determined, when it is determined to be in contact withthe upper boundary, an upper reference line of the current block isdetermined as one reference line, when it is determined not to be incontact with the upper boundary, the upper reference line of the currentblock is determined based on N reference lines, and the determined upperreference line is used, such that the size of a buffer generated when aplurality of reference lines are used may be reduced.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 illustrates a schematic block diagram of an image decodingapparatus according to an embodiment.

FIG. 2 illustrates a flowchart of an image decoding method according toan embodiment.

FIG. 3 illustrates a process, performed by an image decoding apparatus,of determining at least one coding unit by splitting a current codingunit, according to an embodiment.

FIG. 4 illustrates a process, performed by an image decoding apparatus,of determining at least one coding unit by splitting a non-square codingunit, according to an embodiment.

FIG. 5 illustrates a process, performed by an image decoding apparatus,of splitting a coding unit based on at least one of block shapeinformation and split shape mode information, according to anembodiment.

FIG. 6 illustrates a method, performed by an image decoding apparatus,of determining a preset coding unit from among an odd number of codingunits, according to an embodiment.

FIG. 7 illustrates an order of processing a plurality of coding unitswhen an image decoding apparatus determines the plurality of codingunits by splitting a current coding unit, according to an embodiment.

FIG. 8 illustrates a process, performed by an image decoding apparatus,of determining that a current coding unit is to be split into an oddnumber of coding units, when the coding units are not processable in apreset order, according to an embodiment.

FIG. 9 illustrates a process, performed by an image decoding apparatus,of determining at least one coding unit by splitting a first codingunit, according to an embodiment.

FIG. 10 illustrates that a shape into which a second coding unit issplittable is restricted when the second coding unit having a non-squareshape, which is determined when an image decoding apparatus splits afirst coding unit, satisfies a preset condition, according to anembodiment.

FIG. 11 illustrates a process, performed by an image decoding apparatus,of splitting a square coding unit when split shape mode informationindicates that the square coding unit is not to be split into foursquare coding units, according to an embodiment.

FIG. 12 illustrates that a processing order between a plurality ofcoding units may be changed depending on a process of splitting a codingunit, according to an embodiment.

FIG. 13 illustrates a process of determining a depth of a coding unit asa shape and size of the coding unit change, when the coding unit isrecursively split such that a plurality of coding units are determined,according to an embodiment.

FIG. 14 illustrates depths that are determinable based on shapes andsizes of coding units, and part indexes (PIDs) that are fordistinguishing the coding units, according to an embodiment.

FIG. 15 illustrates that a plurality of coding units are determinedbased on a plurality of preset data units included in a picture,according to an embodiment.

FIG. 16 illustrates a processing block serving as a unit for determininga determination order of reference coding units included in a picture,according to an embodiment.

FIG. 17 illustrates a block diagram of a video encoding apparatusaccording to an embodiment.

FIG. 18 illustrates a flowchart of a video encoding method according toan embodiment.

FIG. 19 illustrates a block diagram of a video decoding apparatusaccording to an embodiment.

FIG. 20 illustrates a flowchart of a video decoding method according toan embodiment.

FIG. 21 is a diagram for describing a method of using at least onereference line, according to an embodiment.

FIG. 22 illustrates a flowchart of a video encoding method according toanother embodiment.

FIG. 23 illustrates a flowchart of a video decoding method according toanother embodiment.

FIG. 24A illustrates luma samples located around a current luma blockand a chroma sample located around a current chroma block, according toan embodiment. FIG. 24B illustrates luma samples of a current luma blockand a chroma sample of a current chroma block, according to anembodiment.

FIG. 25A illustrates luma samples located around a current luma blockand a chroma sample located around a current chroma block, according toanother embodiment. FIG. 25B illustrates luma samples of a current lumablock and a chroma sample of a current chroma block, according toanother embodiment.

FIG. 26A illustrates an embodiment in which the number of upperreference lines is different from the number of left reference lines.FIG. 26B illustrates an embodiment in which the number of upperreference lines is the same as the number of left reference lines. FIG.26C illustrates an embodiment in which, when the number of upperreference lines is different from the number of left reference lines,padding is performed so that the number of upper reference lines and thenumber of left reference lines are the same.

BEST MODE

According to an embodiment of the disclosure, a video decoding methodincludes: determining whether a current block is in contact with anupper boundary of a largest coding unit including the current block;when it is determined that the current block is in contact with theupper boundary of the largest coding unit, determining an upperreference line of the current block as one reference line; when it isdetermined that the current block is not in contact with the upperboundary of the largest coding unit, determining the upper referenceline of the current block based on N reference lines; and based on thedetermined upper reference line, performing prediction on the currentblock, wherein N is a natural number.

According to an embodiment, N may be determined according to referenceline information obtained from a bitstream.

According to an embodiment, when it is determined that the current blockis in contact with the upper boundary of the largest coding unit, thereference line information may not be obtained.

According to an embodiment, when N is 2, the upper reference line may bedetermined as a second reference line in contact with an upper side of afirst reference line in contact with an upper side of the current block.

According to an embodiment, when N is 3, the upper reference line may bedetermined as a fourth reference line in contact with an upper side of athird reference line in contact with an upper side of a second referenceline in contact with an upper side of a first reference line in contactwith an upper side of the current block.

According to an embodiment, a left reference line located in a left sideof the current block is determined based on the N reference lines.

According to an embodiment, when a reference line having no sample valueexists in the upper reference line, a sample value of the reference linehaving no sample value may be padded by using a predetermined defaultvalue.

According to an embodiment, when a reference line having no sample valueexists in the upper reference line, a value of a reference sample havingno sample value may be padded with a reference sample having samplevalue, or a sample of the reference line having no sample value may beregenerated by using a sample value of a reference line having a samplevalue.

According to an embodiment of the disclosure, a video decoding methodincludes: determining whether a current luma block is in contact with anupper boundary of a largest coding unit including the current lumablock; when it is determined that the current luma block is in contactwith the upper boundary of the largest coding unit, determining an upperreference line of the current luma block as one reference line; when itis determined that the current luma block is not in contact with theupper boundary of the largest coding unit, determining the upperreference line of the current luma block as two reference lines; andbased on the determined upper reference line, performing prediction on acurrent chroma block corresponding to the current luma block.

According to an embodiment, the two reference lines may include a firstreference line in contact with an upper side of the current luma blockand a second reference line in contact with an upper side of the firstreference line.

According to an embodiment, weight information and deviation informationmay be determined based on a relationship between luma reference samplesof the current luma block included in the upper reference line and achroma reference sample in contact with an upper side of the currentchroma block, and by determining the current chroma block based on theweight information, the deviation information, and luma samples of thecurrent luma block, prediction may be performed on the current chromablock.

According to an embodiment of the disclosure, a video encoding methodincludes: determining whether a current block is in contact with anupper boundary of a largest coding unit including the current block;when it is determined that the current block is in contact with theupper boundary of the largest coding unit, determining an upperreference line of the current block as one reference line; when it isdetermined that the current block is not in contact with the upperboundary of the largest coding unit, determining the upper referenceline of the current block based on N reference lines; and based on thedetermined upper reference line, performing prediction on the currentblock, wherein N is a natural number.

According to an embodiment, the video encoding method may furtherinclude generating reference line information indicating a value of N.

According to an embodiment, when it is determined that the current blockis in contact with the upper boundary of the largest coding unit, thereference line information may not be generated.

According to an embodiment, when N is 3, the upper reference line may bedetermined as a fourth reference line in contact with an upper side of athird reference line in contact with an upper side of a second referenceline in contact with an upper side of a first reference line in contactwith an upper side of the current block.

MODE OF DISCLOSURE

The advantages and features of the disclosure and methods of achievingthe advantages and features will be described more fully with referenceto the accompanying drawings, in which embodiments of the disclosure areshown. The disclosure may, however, be embodied in many different formsand should not be construed as being limited to the embodiments setforth herein; rather these embodiments are provided so that thedisclosure will be thorough and complete, and will fully convey theconcept of the disclosure to one of ordinary skill in the art.

The terms used herein will be briefly described, and disclosedembodiments will be described in detail.

The terms used herein are those general terms currently widely used inthe art in consideration of functions in the disclosure, but the termsmay vary according to the intention of one of ordinary skill in the art,precedents, or new technology in the art. Also, some of the terms usedherein may be arbitrarily chosen by the present applicant, and in thiscase, these terms are defined in detail below. Accordingly, the specificterms used herein should be defined based on the unique meanings thereofand the whole context of the disclosure.

It is to be understood that the singular forms “a,” “an,” and “the”include plural referents unless the context clearly dictates otherwise.

It will be understood that when a certain part “includes” a certaincomponent, the part does not exclude another component but may furtherinclude another component, unless the context clearly dictatesotherwise.

Also, the term “˜unit” used herein refers to a software component or ahardware component, which performs certain tasks. However, the term“˜unit” is not limited to software or hardware. A “˜unit” may beconfigured to be in an addressable storage medium or configured tooperate one or more processors. Thus, a “˜unit” may include, by way ofexample, components such as software components, object-orientedsoftware components, class components, and task components, processes,functions, attributes, procedures, subroutines, segments of programcode, drivers, firmware, microcode, circuitry, data, databases, datastructures, tables, arrays, and variables. The functionality provided bythe components and “˜units” may be combined into fewer components and“˜units” or further separated into additional components and “˜units”.

According to an embodiment of the disclosure, the “unit” may include aprocessor and a memory. The term “processor” should be interpretedbroadly to include a general purpose processor, a central processingunit (CPU), a microprocessor, a digital signal processor (DSP), acontroller, a microcontroller, a state machine, etc. In somecircumstances, the “processor” may refer to an application specificsemiconductor (ASIC), a programmable logic device (PLD), a fieldprogrammable gate array (FPGA), etc. The term “processor” may refer to acombination of processing devices such as, for example, a combination ofa DSP and a microprocessor, a combination of a plurality ofmicroprocessors, a combination of one or more microprocessors inconjunction with a DSP core, or a combination of any other suchconfiguration.

The term “memory” should be interpreted broadly to include anyelectronic component capable of storing electronic information. The term“memory” may refer to various types of processor-readable media, such asa random access memory (RAM), a read-only memory (ROM), a non-volatilerandom access memory (NVRAM), a programmable read-only memory (PROM), anerase-programmable read-only memory (EPROM), an electrically erasablePROM (EEPROM), a flash memory, a magnetic or optical data storagedevice, a register, etc. When the processor can read information from amemory and/or write information to the memory, the memory is said to bein an electronic communication state with the processor. The memoryintegrated in the processor is in an electronic communication state withthe processor.

Hereinafter, an “image” may indicate a still image of a video or mayindicate a dynamic image such as a moving image, that is, the videoitself.

Hereinafter, a “sample” denotes data assigned to a sampling location ofan image, i.e., data to be processed. For example, pixel values of animage in a spatial domain and transform coefficients on a transformregion may be samples. A unit including at least one such sample may bedefined as a block.

Also, in the present specification, a “current block” may denote a blockof a largest coding unit, a coding unit, a prediction unit, or atransform unit of a current image to be encoded or decoded.

The disclosure will now be described more fully with reference to theaccompanying drawings for one of ordinary skill in the art to be able toperform the disclosure without any difficulty. Also, portions irrelevantto the descriptions of the disclosure will be omitted in the drawingsfor clear descriptions of the disclosure.

Hereinafter, an image encoding apparatus and an image decodingapparatus, and an image encoding method and an image decoding methodaccording to embodiments will be described with reference to FIGS. 1through 16. A method of determining a data unit of an image, accordingto an embodiment, will be described with reference to FIGS. 3 to 16. Avideo encoding/decoding method according to an embodiment will bedescribed below with reference to FIGS. 17 to 21, in which whether acurrent block is in contact with an upper boundary of a largest codingunit including the current block is determined, when it is determinedthat the current block is in contact with the upper boundary, an upperreference line of the current block is determined as one reference line,when it is determined that the current block is not in contact with theupper boundary, the upper reference line of the current block isdetermined based on N reference lines, and prediction on the currentblock is performed based on the determined upper reference line. A videoencoding/decoding method according to another embodiment will bedescribed below with reference to FIGS. 22 to 25, in which whether acurrent luma block is in contact with an upper boundary of a largestcoding unit including the current luma block is determined, when it isdetermined that the current luma block is in contact with the upperboundary, an upper reference line of the current luma block isdetermined as one reference line, when it is determined that the currentluma block is not in contact with the upper boundary, the upperreference line of the current luma block is determined as two referencelines, and prediction on a current chroma block corresponding thecurrent luma block is performed based on the determined upper referenceline. A video encoding/decoding method using a plurality of referencelines, according to an embodiment, will be described below withreference to FIG. 26.

Hereinafter, a method and apparatus for adaptively selecting a contextmodel, based on various shapes of coding units, according to anembodiment of the disclosure, will be described with reference to FIGS.1 and 2.

FIG. 1 illustrates a schematic block diagram of an image decodingapparatus according to an embodiment.

The image decoding apparatus 100 may include a receiver 110 and adecoder 120. The receiver 110 and the decoder 120 may include at leastone processor. Also, the receiver 110 and the decoder 120 may include amemory storing instructions to be performed by the at least oneprocessor.

The receiver 110 may receive a bitstream. The bitstream includesinformation of an image encoded by an image encoding apparatus 2200described below. Also, the bitstream may be transmitted from the imageencoding apparatus 2200. The image encoding apparatus 2200 and the imagedecoding apparatus 100 may be connected via wires or wirelessly, and thereceiver 110 may receive the bitstream via wires or wirelessly. Thereceiver 110 may receive the bitstream from a storage medium, such as anoptical medium or a hard disk. The decoder 120 may reconstruct an imagebased on information obtained from the received bitstream. The decoder120 may obtain, from the bitstream, a syntax element for reconstructingthe image. The decoder 120 may reconstruct the image based on the syntaxelement.

Operations of the image decoding apparatus 100 will be described indetail with reference to FIG. 2.

FIG. 2 illustrates a flowchart of an image decoding method according toan embodiment.

According to an embodiment of the disclosure, the receiver 110 receivesa bitstream.

The image decoding apparatus 100 obtains, from a bitstream, a bin stringcorresponding to a split shape mode of a coding unit (operation 210).The image decoding apparatus 100 determines a split rule of coding units(operation 220). Also, the image decoding apparatus 100 splits thecoding unit into a plurality of coding units, based on at least one ofthe bin string corresponding to the split shape mode and the split rule(operation 230). The image decoding apparatus 100 may determine anallowable first range of a size of the coding unit, according to a ratioof the width and the height of the coding unit, so as to determine thesplit rule. The image decoding apparatus 100 may determine an allowablesecond range of the size of the coding unit, according to the splitshape mode of the coding unit, so as to determine the split rule.

Hereinafter, splitting of a coding unit will be described in detailaccording to an embodiment of the disclosure.

First, one picture may be split into one or more slices or one or moretiles. One slice or one tile may be a sequence of one or more largestcoding units (coding tree units (CTUs)). There is a largest coding block(coding tree block (CTB)) conceptually compared to a largest coding unit(CTU).

The largest coding block (CTB) denotes an N×N block including N×Nsamples (where N is an integer). Each color component may be split intoone or more largest coding blocks.

When a picture has three sample arrays (sample arrays for Y, Cr, and Cbcomponents), a largest coding unit (CTU) includes a largest coding blockof a luma sample, two corresponding largest coding blocks of chromasamples, and syntax structures used to encode the luma sample and thechroma samples. When a picture is a monochrome picture, a largest codingunit includes a largest coding block of a monochrome sample and syntaxstructures used to encode the monochrome samples. When a picture is apicture encoded in color planes separated according to color components,a largest coding unit includes syntax structures used to encode thepicture and samples of the picture.

One largest coding block (CTB) may be split into M×N coding blocksincluding M×N samples (M and N are integers).

When a picture has sample arrays for Y, Cr, and Cb components, a codingunit (CU) includes a coding block of a luma sample, two correspondingcoding blocks of chroma samples, and syntax structures used to encodethe luma sample and the chroma samples. When a picture is a monochromepicture, a coding unit includes a coding block of a monochrome sampleand syntax structures used to encode the monochrome samples. When apicture is a picture encoded in color planes separated according tocolor components, a coding unit includes syntax structures used toencode the picture and samples of the picture.

As described above, a largest coding block and a largest coding unit areconceptually distinguished from each other, and a coding block and acoding unit are conceptually distinguished from each other. That is, a(largest) coding unit refers to a data structure including a (largest)coding block including a corresponding sample and a syntax structurecorresponding to the (largest) coding block. However, because it isunderstood by one of ordinary skill in the art that a (largest) codingunit or a (largest) coding block refers to a block of a preset sizeincluding a preset number of samples, a largest coding block and alargest coding unit, or a coding block and a coding unit are mentionedin the following specification without being distinguished unlessotherwise described.

An image may be split into largest coding units (CTUs). A size of eachlargest coding unit may be determined based on information obtained froma bitstream. A shape of each largest coding unit may be a square shapeof the same size. However, the embodiment is not limited thereto.

For example, information about a maximum size of a luma coding block maybe obtained from a bitstream. For example, the maximum size of the lumacoding block indicated by the information about the maximum size of theluma coding block may be one of 4×4, 8×8, 16×16, 32×32, 64×64, 128×128,and 256×256.

For example, information about a luma block size difference and amaximum size of a luma coding block that may be split into two may beobtained from a bitstream. The information about the luma block sizedifference may refer to a size difference between a luma largest codingunit and a largest luma coding block that may be split into two.Accordingly, when the information about the maximum size of the lumacoding block that may be split into two and the information about theluma block size difference obtained from the bitstream are combined witheach other, a size of the luma largest coding unit may be determined. Asize of a chroma largest coding unit may be determined by using the sizeof the luma largest coding unit. For example, when a Y: Cb: Cr ratio is4:2:0 according to a color format, a size of a chroma block may be halfa size of a luma block, and a size of a chroma largest coding unit maybe half a size of a luma largest coding unit.

According to an embodiment, because information about a maximum size ofa luma coding block that is binary splittable is obtained from abitstream, the maximum size of the luma coding block that is binarysplittable may be variably determined. In contrast, a maximum size of aluma coding block that is ternary splittable may be fixed. For example,the maximum size of the luma coding block that is ternary splittable inan I-picture may be 32×32, and the maximum size of the luma coding blockthat is ternary splittable in a P-picture or a B-picture may be 64×64.

Also, a largest coding unit may be hierarchically split into codingunits based on split shape mode information obtained from a bitstream.At least one of information indicating whether quad splitting isperformed, information indicating whether multi-splitting is performed,split direction information, and split type information may be obtainedas the split shape mode information from the bitstream.

For example, the information indicating whether quad splitting isperformed may indicate whether a current coding unit is quad split(QUAD_SPLIT) or not.

When the current coding unit is not quad split, the informationindicating whether multi-splitting is performed may indicate whether thecurrent coding unit is no longer split (NO_SPLIT) or binary/ternarysplit.

When the current coding unit is binary split or ternary split, the splitdirection information indicates that the current coding unit is split inone of a horizontal direction and a vertical direction.

When the current coding unit is split in the horizontal direction or thevertical direction, the split type information indicates that thecurrent coding unit is binary split or ternary split.

A split mode of the current coding unit may be determined according tothe split direction information and the split type information. A splitmode when the current coding unit is binary split in the horizontaldirection may be determined to be a binary horizontal split mode(SPLIT_BT_HOR), a split mode when the current coding unit is ternarysplit in the horizontal direction may be determined to be a ternaryhorizontal split mode (SPLIT_TT_HOR), a split mode when the currentcoding unit is binary split in the vertical direction may be determinedto be a binary vertical split mode (SPLIT_BT_VER), and a split mode whenthe current coding unit is ternary split in the vertical direction maybe determined to be a ternary vertical split mode (SPLIT_TT_VER).

The image decoding apparatus 100 may obtain, from the bitstream, thesplit shape mode information from one bin string. A form of thebitstream received by the image decoding apparatus 100 may include fixedlength binary code, unary code, truncated unary code, predeterminedbinary code, or the like. The bin string is information in a binarynumber. The bin string may include at least one bit. The image decodingapparatus 100 may obtain the split shape mode information correspondingto the bin string, based on the split rule. The image decoding apparatus100 may determine whether to quad split a coding unit, whether not tosplit a coding unit, a split direction, and a split type, based on onebin string.

The coding unit may be smaller than or the same as the largest codingunit. For example, because a largest coding unit is a coding unit havinga maximum size, the largest coding unit is one of coding units. Whensplit shape mode information about a largest coding unit indicates thatsplitting is not performed, a coding unit determined in the largestcoding unit has the same size as that of the largest coding unit. Whensplit shape mode information about a largest coding unit indicates thatsplitting is performed, the largest coding unit may be split into codingunits. Also, when split shape mode information about a coding unitindicates that splitting is performed, the coding unit may be split intosmaller coding units. However, the splitting of the image is not limitedthereto, and the largest coding unit and the coding unit may not bedistinguished. The splitting of the coding unit will be described indetail with reference to FIGS. 3 through 16.

Also, one or more prediction blocks for prediction may be determinedfrom a coding unit. The prediction block may be the same as or smallerthan the coding unit. Also, one or more transform blocks for transformmay be determined from a coding unit. The transform block may be thesame as or smaller than the coding unit.

The shapes and sizes of the transform block and prediction block may notbe related to each other.

In another embodiment, prediction may be performed by using a codingunit as a prediction unit. Also, transformation may be performed byusing a coding unit as a transform block.

The splitting of the coding unit will be described in detail withreference to FIGS. 3 through 16. A current block and an adjacent blockof the disclosure may indicate one of the largest coding unit, thecoding unit, the prediction block, and the transform block. Also, thecurrent block of the current coding unit is a block that is currentlybeing decoded or encoded or a block that is currently being split. Theadjacent block may be a block reconstructed before the current block.The adjacent block may be adjacent to the current block spatially ortemporally. The adjacent block may be located at one of the lower left,left, upper left, top, upper right, right, lower right of the currentblock.

FIG. 3 illustrates a process, performed by an image decoding apparatus,of determining at least one coding unit by splitting a current codingunit, according to an embodiment.

A block shape may include 4N×4N, 4N×2N, 2N×4N, 4N×N, N×4N, 32N×N, N×32N,16N×N, N×16N, 8N×N, or N×8N. Here, N may be a positive integer. Blockshape information is information indicating at least one of a shape, adirection, a ratio of width and height, or size of a coding unit.

The shape of the coding unit may include a square and a non-square. Whenthe lengths of the width and height of the coding unit are the same(i.e., when the block shape of the coding unit is 4N×4N), the imagedecoding apparatus 100 may determine the block shape information of thecoding unit as a square. The image decoding apparatus 100 may determinethe shape of the coding unit to be a non-square.

When the width and the height of the coding unit are different from eachother (i.e., when the block shape of the coding unit is 4N×2N, 2N×4N,4N×N, N×4N, 32N×N, N×32N, 16N×N, N×16N, 8N×N, or N×8N), the imagedecoding apparatus 100 may determine the block shape information of thecoding unit as a non-square shape. When the shape of the coding unit isnon-square, the image decoding apparatus 100 may determine the ratio ofthe width and height among the block shape information of the codingunit to be at least one of 1:2, 2:1, 1:4, 4:1, 1:8, 8:1, 1:16, 16:1,1:32, and 32:1. Also, the image decoding apparatus 100 may determinewhether the coding unit is in a horizontal direction or a verticaldirection, based on the length of the width and the length of the heightof the coding unit. Also, the image decoding apparatus 100 may determinethe size of the coding unit, based on at least one of the length of thewidth, the length of the height, or the area of the coding unit.

According to an embodiment, the image decoding apparatus 100 maydetermine the shape of the coding unit by using the block shapeinformation, and may determine a splitting method of the coding unit byusing the split shape mode information. That is, a coding unit splittingmethod indicated by the split shape mode information may be determinedbased on a block shape indicated by the block shape information used bythe image decoding apparatus 100.

The image decoding apparatus 100 may obtain the split shape modeinformation from a bitstream. However, an embodiment is not limitedthereto, and the image decoding apparatus 100 and the image encodingapparatus 2200 may determine pre-agreed split shape mode information,based on the block shape information. The image decoding apparatus 100may determine the pre-agreed split shape mode information with respectto a largest coding unit or a smallest coding unit. For example, theimage decoding apparatus 100 may determine split shape mode informationwith respect to the largest coding unit to be a quad split. Also, theimage decoding apparatus 100 may determine split shape mode informationregarding the smallest coding unit to be “not to perform splitting”. Inparticular, the image decoding apparatus 100 may determine the size ofthe largest coding unit to be 256×256. The image decoding apparatus 100may determine the pre-agreed split shape mode information to be a quadsplit. The quad split is a split shape mode in which the width and theheight of the coding unit are both bisected. The image decodingapparatus 100 may obtain a coding unit of a 128×128 size from thelargest coding unit of a 256×256 size, based on the split shape modeinformation. Also, the image decoding apparatus 100 may determine thesize of the smallest coding unit to be 4×4. The image decoding apparatus100 may obtain split shape mode information indicating “not to performsplitting” with respect to the smallest coding unit.

According to an embodiment, the image decoding apparatus 100 may use theblock shape information indicating that the current coding unit has asquare shape. For example, the image decoding apparatus 100 maydetermine whether not to split a square coding unit, whether tovertically split the square coding unit, whether to horizontally splitthe square coding unit, or whether to split the square coding unit intofour coding units, based on the split shape mode information. Referringto FIG. 3, when the block shape information of a current coding unit 300indicates a square shape, the decoder 120 may determine that a codingunit 310 a having the same size as the current coding unit 300 is notsplit, based on the split shape mode information indicating not toperform splitting, or may determine coding units 310 b, 310 c, 310 d,310 e, or 310 f split based on the split shape mode informationindicating a preset splitting method.

Referring to FIG. 3, according to an embodiment, the image decodingapparatus 100 may determine two coding units 310 b obtained by splittingthe current coding unit 300 in a vertical direction, based on the splitshape mode information indicating to perform splitting in a verticaldirection. The image decoding apparatus 100 may determine two codingunits 310 c obtained by splitting the current coding unit 300 in ahorizontal direction, based on the split shape mode informationindicating to perform splitting in a horizontal direction. The imagedecoding apparatus 100 may determine four coding units 310 d obtained bysplitting the current coding unit 300 in vertical and horizontaldirections, based on the split shape mode information indicating toperform splitting in vertical and horizontal directions. According to anembodiment, the image decoding apparatus 100 may determine three codingunits 310 e obtained by splitting the current coding unit 300 in avertical direction, based on the split shape mode information indicatingto perform ternary splitting in a vertical direction. The image decodingapparatus 100 may determine three coding units 310 f obtained bysplitting the current coding unit 300 in a horizontal direction, basedon the split shape mode information indicating to perform ternarysplitting in a horizontal direction. However, splitting methods of thesquare coding unit are not limited to the above- described methods, andthe split shape mode information may indicate various methods. Presetsplitting methods of splitting the square coding unit will be describedin detail below in relation to various embodiments.

FIG. 4 illustrates a process, performed by an image decoding apparatus,of determining at least one coding unit by splitting a non-square codingunit, according to an embodiment.

According to an embodiment, the image decoding apparatus 100 may useblock shape information indicating that a current coding unit has anon-square shape. The image decoding apparatus 100 may determine whethernot to split the non-square current coding unit or whether to split thenon-square current coding unit by using a preset splitting method, basedon split shape mode information. Referring to FIG. 4, when the blockshape information of a current coding unit 400 or 450 indicates anon-square shape, the image decoding apparatus 100 may determine that acoding unit 410 or 460 having the same size as the current coding unit400 or 450 is not split, based on the split shape mode informationindicating not to perform splitting, or determine coding units 420 a and420 b, 430 a to 430 c, 470 a and 470 b, or 480 a to 480 c split based onthe split shape mode information indicating a preset splitting method.Preset splitting methods of splitting a non-square coding unit will bedescribed in detail below in relation to various embodiments.

According to an embodiment, the image decoding apparatus 100 maydetermine a splitting method of a coding unit by using the split shapemode information and, in this case, the split shape mode information mayindicate the number of one or more coding units generated by splitting acoding unit. Referring to FIG. 4, when the split shape mode informationindicates to split the current coding unit 400 or 450 into two codingunits, the image decoding apparatus 100 may determine two coding units420 a and 420 b, or 470 a and 470 b included in the current coding unit400 or 450, by splitting the current coding unit 400 or 450 based on thesplit shape mode information.

According to an embodiment, when the image decoding apparatus 100 splitsthe non-square current coding unit 400 or 450 based on the split shapemode information, the image decoding apparatus 100 may consider thelocation of a long side of the non-square current coding unit 400 or 450to split a current coding unit. For example, the image decodingapparatus 100 may determine a plurality of coding units by splitting thecurrent coding unit 400 or 450 in a direction of splitting a long sideof the current coding unit 400 or 450, in consideration of the shape ofthe current coding unit 400 or 450.

According to an embodiment, when the split shape mode informationindicates to split (ternary split) a coding unit into an odd number ofblocks, the image decoding apparatus 100 may determine an odd number ofcoding units included in the current coding unit 400 or 450. Forexample, when the split shape mode information indicates to split thecurrent coding unit 400 or 450 into three coding units, the imagedecoding apparatus 100 may split the current coding unit 400 or 450 intothree coding units 430 a, 430 b, and 430 c, or 480 a, 480 b, and 480 c.

According to an embodiment, a ratio of the width and height of thecurrent coding unit 400 or 450 may be 4:1 or 1:4. When the ratio of thewidth and height is 4:1, the block shape information may be a horizontaldirection because the length of the width is longer than the length ofthe height. When the ratio of the width and height is 1:4, the blockshape information may be a vertical direction because the length of thewidth is shorter than the length of the height. The image decodingapparatus 100 may determine to split a current coding unit into the oddnumber of blocks, based on the split shape mode information. Also, theimage decoding apparatus 100 may determine a split direction of thecurrent coding unit 400 or 450, based on the block shape information ofthe current coding unit 400 or 450. For example, when the current codingunit 400 is in the vertical direction, the image decoding apparatus 100may determine the coding units 430 a to 430 c by splitting the currentcoding unit 400 in the horizontal direction. Also, when the currentcoding unit 450 is in the horizontal direction, the image decodingapparatus 100 may determine the coding units 480 a to 480 c by splittingthe current coding unit 450 in the vertical direction.

According to an embodiment, the image decoding apparatus 100 maydetermine the odd number of coding units included in the current codingunit 400 or 450, and not all the determined coding units may have thesame size. For example, a preset coding unit 430 b or 480 b from amongthe determined odd number of coding units 430 a, 430 b, and 430 c, or480 a, 480 b, and 480 c may have a size different from the size of theother coding units 430 a and 430 c, or 480 a and 480 c. That is, codingunits which may be determined by splitting the current coding unit 400or 450 may have multiple sizes and, in some cases, all of the odd numberof coding units 430 a, 430 b, and 430 c, or 480 a, 480 b, and 480 c mayhave different sizes.

According to an embodiment, when the split shape mode informationindicates to split a coding unit into the odd number of blocks, theimage decoding apparatus 100 may determine the odd number of codingunits included in the current coding unit 400 or 450, and moreover, mayput a preset restriction on at least one coding unit from among the oddnumber of coding units generated by splitting the current coding unit400 or 450. Referring to FIG. 4, the image decoding apparatus 100 mayset a decoding process regarding the coding unit 430 b or 480 b locatedat the center among the three coding units 430 a, 430 b, and 430 c, or480 a, 480 b, and 480 c generated as the current coding unit 400 or 450is split to be different from that of the other coding units 430 a and430 c, or 480 a and 480 c. For example, the image decoding apparatus 100may restrict the coding unit 430 b or 480 b at the center location to beno longer split or to be split only a preset number of times, unlike theother coding units 430 a and 430 c, or 480 a and 480 c.

FIG. 5 illustrates a process, performed by an image decoding apparatus,of splitting a coding unit based on at least one of block shapeinformation and split shape mode information, according to anembodiment.

According to an embodiment, the image decoding apparatus 100 maydetermine to split or not to split a square first coding unit 500 intocoding units, based on at least one of the block shape information andthe split shape mode information. According to an embodiment, when thesplit shape mode information indicates to split the first coding unit500 in a horizontal direction, the image decoding apparatus 100 maydetermine a second coding unit 510 by splitting the first coding unit500 in a horizontal direction. A first coding unit, a second codingunit, and a third coding unit used according to an embodiment are termsused to understand a relation before and after splitting a coding unit.For example, a second coding unit may be determined by splitting a firstcoding unit, and a third coding unit may be determined by splitting thesecond coding unit. It will be understood that the structure of thefirst coding unit, the second coding unit, and the third coding unitfollows the above descriptions.

According to an embodiment, the image decoding apparatus 100 maydetermine to split or not to split the determined second coding unit 510into coding units, based on the split shape mode information. Referringto FIG. 5, the image decoding apparatus 100 may split the non-squaresecond coding unit 510, which is determined by splitting the firstcoding unit 500, into one or more third coding units 520 a, 520 b, 520c, and 520 d based on at least one of the split shape mode informationand the split shape mode information, or may not split the non-squaresecond coding unit 510. The image decoding apparatus 100 may obtain thesplit shape mode information, and may obtain a plurality ofvarious-shaped second coding units (e.g., 510) by splitting the firstcoding unit 500, based on the obtained split shape mode information, andthe second coding unit 510 may be split by using a splitting method ofthe first coding unit 500 based on the split shape mode information.According to an embodiment, when the first coding unit 500 is split intothe second coding units 510 based on the split shape mode information ofthe first coding unit 500, the second coding unit 510 may also be splitinto the third coding units (e.g., 520 a, or 520 b, 520 c, and 520 d)based on the split shape mode information of the second coding unit 510.That is, a coding unit may be recursively split based on the split shapemode information of each coding unit. Therefore, a square coding unitmay be determined by splitting a non-square coding unit, and anon-square coding unit may be determined by recursively splitting thesquare coding unit.

Referring to FIG. 5, a preset coding unit (e.g., a coding unit locatedat a center location, or a square coding unit) from among an odd numberof third coding units 520 b, 520 c, and 520 d determined by splittingthe non-square second coding unit 510 may be recursively split.According to an embodiment, the square third coding unit 520 c fromamong the odd number of third coding units 520 b, 520 c, and 520 d maybe split in a horizontal direction into a plurality of fourth codingunits. A non-square fourth coding unit 530 b or 530 d from among theplurality of fourth coding units 530 a, 530 b, 530 c, and 530 d may bere-split into a plurality of coding units. For example, the non-squarefourth coding unit 530 b or 530 d may be re-split into an odd number ofcoding units. A method that may be used to recursively split a codingunit will be described below in relation to various embodiments.

According to an embodiment, the image decoding apparatus 100 may spliteach of the third coding units 520 a, or 520 b, 520 c, and 520 d intocoding units, based on the split shape mode information. Also, the imagedecoding apparatus 100 may determine not to split the second coding unit510 based on the split shape mode information. According to anembodiment, the image decoding apparatus 100 may split the non-squaresecond coding unit 510 into the odd number of third coding units 520 b,520 c, and 520 d. The image decoding apparatus 100 may put a presetrestriction on a preset third coding unit from among the odd number ofthird coding units 520 b, 520 c, and 520 d. For example, the imagedecoding apparatus 100 may restrict the third coding unit 520 c at acenter location from among the odd number of third coding units 520 b,520 c, and 520 d to be no longer split or to be split a settable numberof times.

Referring to FIG. 5, the image decoding apparatus 100 may restrict thethird coding unit 520 c, which is at the center location from among theodd number of third coding units 520 b, 520 c, and 520 d included in thenon-square second coding unit 510, to be no longer split, to be split byusing a preset splitting method (e.g., split into only four coding unitsor split by using a splitting method of the second coding unit 510), orto be split only a preset number of times (e.g., split only n times(where n>0)). However, the restrictions on the third coding unit 520 cat the center location are not limited to the above-described examples,and may include various restrictions for decoding the third coding unit520 c at the center location differently from the other third codingunits 520 b and 520 d.

According to an embodiment, the image decoding apparatus 100 may obtainthe split shape mode information, which is used to split a currentcoding unit, from a preset location in the current coding unit.

FIG. 6 illustrates a method, performed by an image decoding apparatus,of determining a preset coding unit from among an odd number of codingunits, according to an embodiment.

Referring to FIG. 6, split shape mode information of a current codingunit 600 or 650 may be obtained from a sample of a preset location(e.g., a sample 640 or 690 of a center location) from among a pluralityof samples included in the current coding unit 600 or 650. However, thepreset location in the current coding unit 600, from which at least onepiece of the split shape mode information may be obtained, is notlimited to the center location in FIG. 6, and may include variouslocations included in the current coding unit 600 (e.g., top, bottom,left, right, upper left, lower left, upper right, lower right locations,or the like). The image decoding apparatus 100 may obtain the splitshape mode information from the preset location and may determine tosplit or not to split the current coding unit into various-shaped andvarious-sized coding units.

According to an embodiment, when the current coding unit is split into apreset number of coding units, the image decoding apparatus 100 mayselect one of the coding units. Various methods may be used to selectone of a plurality of coding units, as will be described below inrelation to various embodiments.

According to an embodiment, the image decoding apparatus 100 may splitthe current coding unit into a plurality of coding units, and maydetermine a coding unit at a preset location.

According to an embodiment, image decoding apparatus 100 may useinformation indicating locations of the odd number of coding units, todetermine a coding unit at a center location from among the odd numberof coding units. Referring to FIG. 6, the image decoding apparatus 100may determine the odd number of coding units 620 a, 620 b, and 620 c orthe odd number of coding units 660 a, 660 b, and 660 c by splitting thecurrent coding unit 600 or the current coding unit 650. The imagedecoding apparatus 100 may determine the middle coding unit 620 b or themiddle coding unit 660 b by using information about the locations of theodd number of coding units 620 a, 620 b, and 620 c or the odd number ofcoding units 660 a, 660 b, and 660 c. For example, the image decodingapparatus 100 may determine the coding unit 620 b of the center locationby determining the locations of the coding units 620 a, 620 b, and 620 cbased on information indicating locations of preset samples included inthe coding units 620 a, 620 b, and 620 c. In detail, the image decodingapparatus 100 may determine the coding unit 620 b at the center locationby determining the locations of the coding units 620 a, 620 b, and 620 cbased on information indicating locations of upper-left samples 630 a,630 b, and 630 c of the coding units 620 a, 620 b, and 620 c.

According to an embodiment, the information indicating the locations ofthe upper-left samples 630 a, 630 b, and 630 c, which are included inthe coding units 620 a, 620 b, and 620 c, respectively, may includeinformation about locations or coordinates of the coding units 620 a,620 b, and 620 c in a picture. According to an embodiment, theinformation indicating the locations of the upper-left samples 630 a,630 b, and 630 c, which are included in the coding units 620 a, 620 b,and 620 c, respectively, may include information indicating widths orheights of the coding units 620 a, 620 b, and 620 c included in thecurrent coding unit 600, and the widths or heights may correspond toinformation indicating differences between the coordinates of the codingunits 620 a, 620 b, and 620 c in the picture. That is, the imagedecoding apparatus 100 may determine the coding unit 620 b at the centerlocation by directly using the information about the locations orcoordinates of the coding units 620 a, 620 b, and 620 c in the picture,or by using the information about the widths or heights of the codingunits, which correspond to the difference values between thecoordinates.

According to an embodiment, information indicating the location of theupper-left sample 630 a of the upper coding unit 620 a may includecoordinates (xa, ya), information indicating the location of theupper-left sample 630 b of the middle coding unit 620 b may includecoordinates (xb, yb), and information indicating the location of theupper-left sample 630 c of the lower coding unit 620 c may includecoordinates (xc, yc). The image decoding apparatus 100 may determine themiddle coding unit 620 b by using the coordinates of the upper-leftsamples 630 a, 630 b, and 630 c which are included in the coding units620 a, 620 b, and 620 c, respectively. For example, when the coordinatesof the upper-left samples 630 a, 630 b, and 630 c are sorted in anascending or descending order, the coding unit 620 b including thecoordinates (xb, yb) of the sample 630 b at a center location may bedetermined as a coding unit at a center location from among the codingunits 620 a, 620 b, and 620 c determined by splitting the current codingunit 600. However, the coordinates indicating the locations of theupper-left samples 630 a, 630 b, and 630 c may include coordinatesindicating absolute locations in the picture, or may use coordinates(dxb, dyb) indicating a relative location of the upper-left sample 630 bof the middle coding unit 620 b and coordinates (dxc, dyc) indicating arelative location of the upper-left sample 630 c of the lower codingunit 620 c with reference to the location of the upper-left sample 630 aof the upper coding unit 620 a. A method of determining a coding unit ata preset location by using coordinates of a sample included in thecoding unit, as information indicating a location of the sample, is notlimited to the above-described method, and may include variousarithmetic methods capable of using the coordinates of the sample.

According to an embodiment, the image decoding apparatus 100 may splitthe current coding unit 600 into a plurality of coding units 620 a, 620b, and 620 c, and may select one of the coding units 620 a, 620 b, and620 c based on a preset criterion. For example, the image decodingapparatus 100 may select the coding unit 620 b, which has a sizedifferent from that of the others, from among the coding units 620 a,620 b, and 620 c.

According to an embodiment, the image decoding apparatus 100 maydetermine the width or height of each of the coding units 620 a, 620 b,and 620 c by using the coordinates (xa, ya) that is the informationindicating the location of the upper-left sample 630 a of the uppercoding unit 620 a, the coordinates (xb, yb) that is the informationindicating the location of the upper-left sample 630 b of the middlecoding unit 620 b, and the coordinates (xc, yc) that is the informationindicating the location of the upper-left sample 630 c of the lowercoding unit 620 c. The image decoding apparatus 100 may determine therespective sizes of the coding units 620 a, 620 b, and 620 c by usingthe coordinates (xa, ya), (xb, yb), and (xc, yc) indicating thelocations of the coding units 620 a, 620 b, and 620 c. According to anembodiment, the image decoding apparatus 100 may determine the width ofthe upper coding unit 620 a to be the width of the current coding unit600. The image decoding apparatus 100 may determine the height of theupper coding unit 620 a to be yb−ya. According to an embodiment, theimage decoding apparatus 100 may determine the width of the middlecoding unit 620 b to be the width of the current coding unit 600. Theimage decoding apparatus 100 may determine the height of the middlecoding unit 620 b to be yc−yb. According to an embodiment, the imagedecoding apparatus 100 may determine the width or height of the lowercoding unit 620 c by using the width or height of the current codingunit 600 or the widths or heights of the upper and middle coding units620 a and 620 b. The image decoding apparatus 100 may determine a codingunit, which has a size different from that of the others, based on thedetermined widths and heights of the coding units 620 a to 620 c.Referring to FIG. 6, the image decoding apparatus 100 may determine themiddle coding unit 620 b, which has a size different from the size ofthe upper and lower coding units 620 a and 620 c, as the coding unit ofthe preset location. However, the above-described method, performed bythe image decoding apparatus 100, of determining a coding unit having asize different from the size of the other coding units merelycorresponds to an example of determining a coding unit at a presetlocation by using the sizes of coding units, which are determined basedon coordinates of samples, and thus various methods of determining acoding unit at a preset location by comparing the sizes of coding units,which are determined based on coordinates of preset samples, may beused.

The image decoding apparatus 100 may determine the width or height ofeach of the coding units 660 a, 660 b, and 660 c by using thecoordinates (xd, yd) that is information indicating the location of anupper-left sample 670 a of the left coding unit 660 a, the coordinates(xe, ye) that is information indicating the location of an upper-leftsample 670 b of the middle coding unit 660 b, and the coordinates (xf,yf) that is information indicating a location of the upper-left sample670 c of the right coding unit 660 c. The image decoding apparatus 100may determine the respective sizes of the coding units 660 a, 660 b, and660 c by using the coordinates (xd, yd), (xe, ye), and (xf, yf)indicating the locations of the coding units 660 a, 660 b, and 660 c.

According to an embodiment, the image decoding apparatus 100 maydetermine the width of the left coding unit 660 a to be xe−xd. The imagedecoding apparatus 100 may determine the height of the left coding unit660 a to be the height of the current coding unit 650. According to anembodiment, the image decoding apparatus 100 may determine the width ofthe middle coding unit 660 b to be xf−xe. The image decoding apparatus100 may determine the height of the middle coding unit 660 b to be theheight of the current coding unit 650. According to an embodiment, theimage decoding apparatus 100 may determine the width or height of theright coding unit 660 c by using the width or height of the currentcoding unit 650 or the widths or heights of the left and middle codingunits 660 a and 660 b. The image decoding apparatus 100 may determine acoding unit, which has a size different from that of the others, basedon the determined widths and heights of the coding units 660 a to 660 c.Referring to FIG. 6, the image decoding apparatus 100 may determine themiddle coding unit 660 b, which has a size different from the sizes ofthe left and right coding units 660 a and 660 c, as the coding unit ofthe preset location. However, the above-described method, performed bythe image decoding apparatus 100, of determining a coding unit having asize different from the size of the other coding units merelycorresponds to an example of determining a coding unit at a presetlocation by using the sizes of coding units, which are determined basedon coordinates of samples, and thus various methods of determining acoding unit at a preset location by comparing the sizes of coding units,which are determined based on coordinates of preset samples, may beused.

However, locations of samples considered to determine locations ofcoding units are not limited to the above-described upper leftlocations, and information about arbitrary locations of samples includedin the coding units may be used.

According to an embodiment, the image decoding apparatus 100 may selecta coding unit at a preset location from among an odd number of codingunits determined by splitting the current coding unit, considering theshape of the current coding unit. For example, when the current codingunit has a non-square shape, a width of which is longer than a height,the image decoding apparatus 100 may determine the coding unit at thepreset location in a horizontal direction. That is, the image decodingapparatus 100 may determine one of coding units at different locationsin a horizontal direction and put a restriction on the coding unit. Whenthe current coding unit has a non-square shape, a height of which islonger than a width, the image decoding apparatus 100 may determine thecoding unit at the preset location in a vertical direction. That is, theimage decoding apparatus 100 may determine one of coding units atdifferent locations in a vertical direction and may put a restriction onthe coding unit.

According to an embodiment, the image decoding apparatus 100 may useinformation indicating respective locations of an even number of codingunits, to determine the coding unit at the preset location from amongthe even number of coding units. The image decoding apparatus 100 maydetermine an even number of coding units by splitting (binary splitting)the current coding unit, and may determine the coding unit at the presetlocation by using the information about the locations of the even numberof coding units. An operation related thereto may correspond to theoperation of determining a coding unit at a preset location (e.g., acenter location) from among an odd number of coding units, which hasbeen described in detail above in relation to FIG. 6, and thus detaileddescriptions thereof are not provided here.

According to an embodiment, when a non-square current coding unit issplit into a plurality of coding units, preset information about acoding unit at a preset location may be used in a splitting operation todetermine the coding unit at the preset location from among theplurality of coding units. For example, the image decoding apparatus 100may use at least one of block shape information and split shape modeinformation, which is stored in a sample included in a middle codingunit, in a splitting operation to determine a coding unit at a centerlocation from among the plurality of coding units determined bysplitting the current coding unit.

Referring to FIG. 6, the image decoding apparatus 100 may split thecurrent coding unit 600 into the plurality of coding units 620 a, 620 b,and 620 c based on the split shape mode information, and may determinethe coding unit 620 b at a center location from among the plurality ofthe coding units 620 a, 620 b, and 620 c. Furthermore, the imagedecoding apparatus 100 may determine the coding unit 620 b at the centerlocation, in consideration of a location from which the split shape modeinformation is obtained. That is, the split shape mode information ofthe current coding unit 600 may be obtained from the sample 640 at acenter location of the current coding unit 600 and, when the currentcoding unit 600 is split into the plurality of coding units 620 a, 620b, and 620 c based on the split shape mode information, the coding unit620 b including the sample 640 may be determined as the coding unit atthe center location. However, information used to determine the codingunit at the center location is not limited to the split shape modeinformation, and various types of information may be used to determinethe coding unit at the center location.

According to an embodiment, preset information for identifying thecoding unit at the preset location may be obtained from a preset sampleincluded in a coding unit to be determined. Referring to FIG. 6, theimage decoding apparatus 100 may use the split shape mode information,which is obtained from a sample at a preset location in the currentcoding unit 600 (e.g., a sample at a center location of the currentcoding unit 600) to determine a coding unit at a preset location fromamong the plurality of the coding units 620 a, 620 b, and 620 cdetermined by splitting the current coding unit 600 (e.g., a coding unitat a center location from among a plurality of split coding units). Thatis, the image decoding apparatus 100 may determine the sample at thepreset location by considering a block shape of the current coding unit600, determine the coding unit 620 b including a sample, from whichpreset information (e.g., the split shape mode information) may beobtained, from among the plurality of coding units 620 a, 620 b, and 620c determined by splitting the current coding unit 600, and may put apreset restriction on the coding unit 620 b. Referring to FIG. 6,according to an embodiment, the image decoding apparatus 100 maydetermine the sample 640 at the center location of the current codingunit 600 as the sample from which the preset information may beobtained, and may put a preset restriction on the coding unit 620 bincluding the sample 640, in a decoding operation. However, the locationof the sample from which the preset information may be obtained is notlimited to the above-described location, and may include arbitrarylocations of samples included in the coding unit 620 b to be determinedfor a restriction.

According to an embodiment, the location of the sample from which thepreset information may be obtained may be determined based on the shapeof the current coding unit 600. According to an embodiment, the blockshape information may indicate whether the current coding unit has asquare or non-square shape, and the location of the sample from whichthe preset information may be obtained may be determined based on theshape. For example, the image decoding apparatus 100 may determine asample located on a boundary for splitting at least one of a width andheight of the current coding unit in half, as the sample from which thepreset information may be obtained, by using at least one of informationabout the width of the current coding unit and information about theheight of the current coding unit. As another example, when the blockshape information of the current coding unit indicates a non-squareshape, the image decoding apparatus 100 may determine one of samplesadjacent to a boundary for splitting a long side of the current codingunit in half, as the sample from which the preset information may beobtained.

According to an embodiment, when the current coding unit is split into aplurality of coding units, the image decoding apparatus 100 may use thesplit shape mode information to determine a coding unit at a presetlocation from among the plurality of coding units. According to anembodiment, the image decoding apparatus 100 may obtain the split shapemode information from a sample at a preset location in a coding unit,and split the plurality of coding units, which are generated bysplitting the current coding unit, by using the split shape modeinformation, which is obtained from the sample of the preset location ineach of the plurality of coding units. That is, a coding unit may berecursively split based on the split shape mode information, which isobtained from the sample at the preset location in each coding unit. Anoperation of recursively splitting a coding unit has been describedabove in relation to FIG. 5, and thus detailed descriptions thereof willnot be provided here.

According to an embodiment, the image decoding apparatus 100 maydetermine one or more coding units by splitting the current coding unit,and may determine an order of decoding the one or more coding units,based on a preset block (e.g., the current coding unit).

FIG. 7 illustrates an order of processing a plurality of coding unitswhen an image decoding apparatus determines the plurality of codingunits by splitting a current coding unit, according to an embodiment.

According to an embodiment, the image decoding apparatus 100 maydetermine second coding units 710 a and 710 b by splitting a firstcoding unit 700 in a vertical direction, determine second coding units730 a and 730 b by splitting the first coding unit 700 in a horizontaldirection, or determine second coding units 750 a to 750 d by splittingthe first coding unit 700 in vertical and horizontal directions, basedon split shape mode information.

Referring to FIG. 7, the image decoding apparatus 100 may determine toprocess the second coding units 710 a and 710 b, which are determined bysplitting the first coding unit 700 in a vertical direction, in ahorizontal direction order 710 c. The image decoding apparatus 100 maydetermine to process the second coding units 730 a and 730 b, which aredetermined by splitting the first coding unit 700 in a horizontaldirection, in a vertical direction order 730 c. The image decodingapparatus 100 may determine the second coding units 750 a to 750 d,which are determined by splitting the first coding unit 700 in verticaland horizontal directions, according to a preset order (e.g., a rasterscan order or Z-scan order 750 e) by which coding units in a row areprocessed and then coding units in a next row are processed.

According to an embodiment, the image decoding apparatus 100 mayrecursively split coding units. Referring to FIG. 7, the image decodingapparatus 100 may determine the plurality of coding units 710 a and 710b, 730 a and 730 b, or 750 a to 750 d by splitting the first coding unit700, and recursively split each of the determined plurality of codingunits 710 a, 710 b, 730 a, 730 b, 750 a, 750 b, 750 c, and 750 d. Asplitting method of the plurality of coding units 710 a and 710 b, 730 aand 730 b, or 750 a to 750 d may correspond to a splitting method of thefirst coding unit 700. As such, each of the plurality of coding units710 a and 710 b, 730 a and 730 b, or 750 a to 750 d may be independentlysplit into a plurality of coding units. Referring to FIG. 7, the imagedecoding apparatus 100 may determine the second coding units 710 a and710 b by splitting the first coding unit 700 in a vertical direction,and may determine to independently split or not to split each of thesecond coding units 710 a and 710 b.

According to an embodiment, the image decoding apparatus 100 maydetermine third coding units 720 a and 720 b by splitting the leftsecond coding unit 710 a in a horizontal direction, and may not splitthe right second coding unit 710 b.

According to an embodiment, a processing order of coding units may bedetermined based on an operation of splitting a coding unit. In otherwords, a processing order of split coding units may be determined basedon a processing order of coding units immediately before being split.The image decoding apparatus 100 may determine a processing order of thethird coding units 720 a and 720 b determined by splitting the leftsecond coding unit 710 a, independently of the right second coding unit710 b. Because the third coding units 720 a and 720 b are determined bysplitting the left second coding unit 710 a in a horizontal direction,the third coding units 720 a and 720 b may be processed in a verticaldirection order 720 c. Because the left and right second coding units710 a and 710 b are processed in the horizontal direction order 710 c,the right second coding unit 710 b may be processed after the thirdcoding units 720 a and 720 b included in the left second coding unit 710a are processed in the vertical direction order 720 c. An operation ofdetermining a processing order of coding units based on a coding unitbefore being split is not limited to the above-described example, andvarious methods may be used to independently process coding units, whichare split and determined to various shapes, in a preset order.

FIG. 8 illustrates a process, performed by an image decoding apparatus,of determining that a current coding unit is to be split into an oddnumber of coding units, when the coding units are not processable in apreset order, according to an embodiment.

According to an embodiment, the image decoding apparatus 100 maydetermine that the current coding unit is split into an odd number ofcoding units, based on obtained split shape mode information. Referringto FIG. 8, a square first coding unit 800 may be split into non-squaresecond coding units 810 a and 810 b, and the second coding units 810 aand 810 b may be independently split into third coding units 820 a and820 b, and 820 c to 820 e. According to an embodiment, the imagedecoding apparatus 100 may determine the plurality of third coding units820 a and 820 b by splitting the left second coding unit 810 a in ahorizontal direction, and may split the right second coding unit 810 binto the odd number of third coding units 820 c to 820 e.

According to an embodiment, the video decoding apparatus 100 maydetermine whether any coding unit is split into an odd number of codingunits, by determining whether the third coding units 820 a and 820 b,and 820 c to 820 e are processable in a preset order. Referring to FIG.8, the image decoding apparatus 100 may determine the third coding units820 a and 820 b, and 820 c to 820 e by recursively splitting the firstcoding unit 800. The image decoding apparatus 100 may determine whetherany of the first coding unit 800, the second coding units 810 a and 810b, or the third coding units 820 a and 820 b, and 820 c to 820 e aresplit into an odd number of coding units, based on at least one of theblock shape information and the split shape mode information. Forexample, a coding unit located in the right from among the second codingunits 810 a and 810 b may be split into an odd number of third codingunits 820 c, 820 d, and 820 e. A processing order of a plurality ofcoding units included in the first coding unit 800 may be a preset order(e.g., a Z-scan order 830), and the image decoding apparatus 100 maydetermine whether the third coding units 820 c, 820 d, and 820 e, whichare determined by splitting the right second coding unit 810 b into anodd number of coding units, satisfy a condition for processing in thepreset order.

According to an embodiment, the image decoding apparatus 100 maydetermine whether the third coding units 820 a and 820 b, and 820 c to820 e included in the first coding unit 800 satisfy the condition forprocessing in the preset order, and the condition relates to whether atleast one of a width and height of the second coding units 810 a and 810b is to be split in half along a boundary of the third coding units 820a and 820 b, and 820 c to 820 e. For example, the third coding units 820a and 820 b determined when the height of the left second coding unit810 a of the non-square shape is split in half may satisfy thecondition. It may be determined that the third coding units 820 c to 820e do not satisfy the condition because the boundaries of the thirdcoding units 820 c to 820 e determined when the right second coding unit810 b is split into three coding units are unable to split the width orheight of the right second coding unit 810 b in half. When the conditionis not satisfied as described above, the image decoding apparatus 100may determine disconnection of a scan order, and may determine that theright second coding unit 810 b is to be split into an odd number ofcoding units, based on a result of the determination. According to anembodiment, when a coding unit is split into an odd number of codingunits, the image decoding apparatus 100 may put a preset restriction ona coding unit at a preset location from among the split coding units.The restriction or the preset location has been described above inrelation to various embodiments, and thus detailed descriptions thereofwill not be provided herein.

FIG. 9 illustrates a process, performed by an image decoding apparatus,of determining at least one coding unit by splitting a first codingunit, according to an embodiment.

According to an embodiment, the image decoding apparatus 100 may splitthe first coding unit 900, based on split shape mode information, whichis obtained through the receiver 110. The square first coding unit 900may be split into four square coding units, or may be split into aplurality of non-square coding units. For example, referring to FIG. 9,when the first coding unit 900 has a square shape and the split shapemode information indicates to split the first coding unit 900 intonon-square coding units, the image decoding apparatus 100 may split thefirst coding unit 900 into a plurality of non-square coding units. Indetail, when the split shape mode information indicates to determine anodd number of coding units by splitting the first coding unit 900 in ahorizontal direction or a vertical direction, the image decodingapparatus 100 may split the square first coding unit 900 into an oddnumber of coding units, e.g., second coding units 910 a, 910 b, and 910c determined by splitting the square first coding unit 900 in a verticaldirection or second coding units 920 a, 920 b, and 920 c determined bysplitting the square first coding unit 900 in a horizontal direction.

According to an embodiment, the image decoding apparatus 100 maydetermine whether the second coding units 910 a, 910 b, 910 c, 920 a,920 b, and 920 c included in the first coding unit 900 satisfy acondition for processing in a preset order, and the condition relates towhether at least one of a width and height of the first coding unit 900is to be split in half along a boundary of the second coding units 910a, 910 b, 910 c, 920 a, 920 b, and 920 c. Referring to FIG. 9, becauseboundaries of the second coding units 910 a, 910 b, and 910 c determinedby splitting the square first coding unit 900 in a vertical direction donot split the height of the first coding unit 900 in half, it may bedetermined that the first coding unit 900 does not satisfy the conditionfor processing in the preset order. Also, because boundaries of thesecond coding units 920 a, 920 b, and 920 c determined by splitting thesquare first coding unit 900 in a horizontal direction do not split thewidth of the first coding unit 900 in half, it may be determined thatthe first coding unit 900 does not satisfy the condition for processingin the preset order. When the condition is not satisfied as describedabove, the image decoding apparatus 100 may decide disconnection of ascan order, and may determine that the first coding unit 900 is to besplit into an odd number of coding units, based on a result of thedecision. According to an embodiment, when a coding unit is split intoan odd number of coding units, the image decoding apparatus 100 may puta preset restriction on a coding unit at a preset location from amongthe split coding units. The restriction or the preset location has beendescribed above in relation to various embodiments, and thus detaileddescriptions thereof will not be provided herein.

According to an embodiment, the image decoding apparatus 100 maydetermine various-shaped coding units by splitting a first coding unit.

Referring to FIG. 9, the image decoding apparatus 100 may split thesquare first coding unit 900 or a non-square first coding unit 930 or950 into various-shaped coding units.

FIG. 10 illustrates that a shape into which a second coding unit issplittable is restricted when the second coding unit having a non-squareshape, which is determined when an image decoding apparatus splits afirst coding unit, satisfies a preset condition, according to anembodiment.

According to an embodiment, the image decoding apparatus 100 maydetermine to split the square first coding unit 1000 into non-squaresecond coding units 1010 a, and 1010 b or 1020 a and 1020 b, based onsplit shape mode information, which is obtained by the receiver 110. Thesecond coding units 1010 a and 1010 b, or 1020 a and 1020 b may beindependently split. As such, the image decoding apparatus 100 maydetermine to split or not to split each of the second coding units 1010a and 1010 b, or 1020 a and 1020 b into a plurality of coding units,based on the split shape mode information of each of the second codingunits 1010 a and 1010 b, or 1020 a and 1020 b. According to anembodiment, the image decoding apparatus 100 may determine third codingunits 1012 a and 1012 b by splitting the non-square left second codingunit 1010 a, which is determined by splitting the first coding unit 1000in a vertical direction, in a horizontal direction. However, when theleft second coding unit 1010 a is split in a horizontal direction, theimage decoding apparatus 100 may restrict the right second coding unit1010 b to not be split in a horizontal direction in which the leftsecond coding unit 1010 a is split. When third coding units 1014 a and1014 b are determined by splitting the right second coding unit 1010 bin a same direction, because the left and right second coding units 1010a and 1010 b are independently split in a horizontal direction, thethird coding units 1012 a and 1012 b, or 1014 a and 1014 b may bedetermined. However, this case serves equally as a case in which theimage decoding apparatus 100 splits the first coding unit 1000 into foursquare second coding units 1030 a, 1030 b, 1030 c, and 1030 d, based onthe split shape mode information, and may be inefficient in terms ofimage decoding.

According to an embodiment, the image decoding apparatus 100 maydetermine third coding units 1022 a and 1022 b, or 1024 a and 1024 b bysplitting the non-square second coding unit 1020 a or 1020 b, which isdetermined by splitting the first coding unit 1000 in a horizontaldirection, in a vertical direction. However, when a second coding unit(e.g., the upper second coding unit 1020 a) is split in a verticaldirection, for the above-described reason, the image decoding apparatus100 may restrict the other second coding unit (e.g., the lower secondcoding unit 1020 b) to not be split in a vertical direction in which theupper second coding unit 1020 a is split.

FIG. 11 illustrates a process, performed by an image decoding apparatus,of splitting a square coding unit when split shape mode informationindicates that the square coding unit is not to be split into foursquare coding units, according to an embodiment.

According to an embodiment, the image decoding apparatus 100 maydetermine second coding units 1110 a and 1110 b, or 1120 a and 1120 b,etc. by splitting a first coding unit 1100, based on split shape modeinformation. The split shape mode information may include informationabout various methods of splitting a coding unit but, the informationabout various splitting methods may not include information forsplitting a coding unit into four square coding units. According to suchsplit shape mode information, the image decoding apparatus 100 may notsplit the square first coding unit 1100 into four square second codingunits 1130 a, 1130 b, 1130 c, and 1130 d. The image decoding apparatus100 may determine the non-square second coding units 1110 a and 1110 b,or 1120 a and 1120 b, etc., based on the split shape mode information.

According to an embodiment, the image decoding apparatus 100 mayindependently split the non-square second coding units 1110 a and 1110b, or 1120 a and 1120 b, etc. Each of the second coding units 1110 a and1110 b, or 1120 a and 1120 b, etc. may be recursively split in a presetorder, and this splitting method may correspond to a method of splittingthe first coding unit 1100, based on the split shape mode information.

For example, the image decoding apparatus 100 may determine square thirdcoding units 1112 a and 1112 b by splitting the left second coding unit1110 a in a horizontal direction, and may determine square third codingunits 1114 a and 1114 b by splitting the right second coding unit 1110 bin a horizontal direction. Furthermore, the image decoding apparatus 100may determine square third coding units 1116 a, 1116 b, 1116 c, and 1116d by splitting both of the left and right second coding units 1110 a and1110 b in a horizontal direction. In this case, coding units having thesame shape as the four square second coding units 1130 a, 1130 b, 1130c, and 1130 d split from the first coding unit 1100 may be determined.

As another example, the image decoding apparatus 100 may determinesquare third coding units 1122 a and 1122 b by splitting the uppersecond coding unit 1120 a in a vertical direction, and may determinesquare third coding units 1124 a and 1124 b by splitting the lowersecond coding unit 1120 b in a vertical direction. Furthermore, theimage decoding apparatus 100 may determine square third coding units1126 a, 1126 b, 1126 c, and 1126 d by splitting both of the upper andlower second coding units 1120 a and 1120 b in a vertical direction. Inthis case, coding units having the same shape as the four square secondcoding units 1130 a, 1130 b, 1130 c, and 1130 d split from the firstcoding unit 1100 may be determined.

FIG. 12 illustrates that a processing order between a plurality ofcoding units may be changed depending on a process of splitting a codingunit, according to an embodiment.

According to an embodiment, the image decoding apparatus 100 may split afirst coding unit 1200, based on split shape mode information. When ablock shape indicates a square shape and the split shape modeinformation indicates to split the first coding unit 1200 in at leastone of horizontal and vertical directions, the image decoding apparatus100 may determine second coding units 1210 a and 1210 b, or 1220 a and1220 b, etc. by splitting the first coding unit 1200. Referring to FIG.12, the non-square second coding units 1210 a and 1210 b, or 1220 a and1220 b determined by splitting the first coding unit 1200 in only ahorizontal direction or vertical direction may be independently splitbased on the split shape mode information of each coding unit. Forexample, the image decoding apparatus 100 may determine third codingunits 1216 a, 1216 b, 1216 c, and 1216 d by splitting the second codingunits 1210 a and 1210 b, which are generated by splitting the firstcoding unit 1200 in a vertical direction, in a horizontal direction, andmay determine third coding units 1226 a, 1226 b, 1226 c, and 1226 d bysplitting the second coding units 1220 a and 1220 b, which are generatedby splitting the first coding unit 1200 in a horizontal direction, in avertical direction. An operation of splitting the second coding units1210 a and 1210 b, or 1220 a and 1220 b has been described above inrelation to FIG. 11, and thus detailed descriptions thereof will not beprovided herein.

According to an embodiment, the image decoding apparatus 100 may processcoding units in a preset order. An operation of processing coding unitsin a preset order has been described above in relation to FIG. 7, andthus detailed descriptions thereof will not be provided herein.Referring to FIG. 12, the image decoding apparatus 100 may determinefour square third coding units 1216 a, 1216 b, 1216 c, and 1216 d, and1226 a, 1226 b, 1226 c, and 1226 d by splitting the square first codingunit 1200. According to an embodiment, the image decoding apparatus 100may determine processing orders of the third coding units 1216 a, 1216b, 1216 c, and 1216 d, and 1226 a, 1226 b, 1226 c, and 1226 d based on asplit shape by which the first coding unit 1200 is split.

According to an embodiment, the image decoding apparatus 100 maydetermine the third coding units 1216 a, 1216 b, 1216 c, and 1216 d bysplitting the second coding units 1210 a and 1210 b generated bysplitting the first coding unit 1200 in a vertical direction, in ahorizontal direction, and may process the third coding units 1216 a,1216 b, 1216 c, and 1216 d in a processing order 1217 for initiallyprocessing the third coding units 1216 a and 1216 c, which are includedin the left second coding unit 1210 a, in a vertical direction and thenprocessing the third coding unit 1216 b and 1216 d, which are includedin the right second coding unit 1210 b, in a vertical direction.

According to an embodiment, the image decoding apparatus 100 maydetermine the third coding units 1226 a, 1226 b, 1226 c, and 1226 d bysplitting the second coding units 1220 a and 1220 b generated bysplitting the first coding unit 1200 in a horizontal direction, in avertical direction, and may process the third coding units 1226 a, 1226b, 1226 c, and 1226 d in a processing order 1227 for initiallyprocessing the third coding units 1226 a and 1226 b, which are includedin the upper second coding unit 1220 a, in a horizontal direction andthen processing the third coding unit 1226 c and 1226 d, which areincluded in the lower second coding unit 1220 b, in a horizontaldirection.

Referring to FIG. 12, the square third coding units 1216 a, 1216 b, 1216c, and 1216 d, and 1226 a, 1226 b, 1226 c, and 1226 d may be determinedby splitting the second coding units 1210 a and 1210 b, and 1220 a and1220 b, respectively. Although the second coding units 1210 a and 1210 bare determined by splitting the first coding unit 1200 in a verticaldirection differently from the second coding units 1220 a and 1220 bwhich are determined by splitting the first coding unit 1200 in ahorizontal direction, the third coding units 1216 a, 1216 b, 1216 c, and1216 d, and 1226 a, 1226 b, 1226 c, and 1226 d split therefromeventually show same-shaped coding units split from the first codingunit 1200. As such, by recursively splitting a coding unit in differentmanners based on the split shape mode information, the image decodingapparatus 100 may process a plurality of coding units in differentorders even when the coding units are eventually determined to be thesame shape.

FIG. 13 illustrates a process of determining a depth of a coding unit asa shape and size of the coding unit change, when the coding unit isrecursively split such that a plurality of coding units are determined,according to an embodiment.

According to an embodiment, the image decoding apparatus 100 maydetermine the depth of the coding unit, based on a preset criterion. Forexample, the preset criterion may be the length of a long side of thecoding unit. When the length of a long side of a coding unit beforebeing split is 2n times (n>0) the length of a long side of a splitcurrent coding unit, the image decoding apparatus 100 may determine thata depth of the current coding unit is increased from a depth of thecoding unit before being split, by n. In the following description, acoding unit having an increased depth is expressed as a coding unit of adeeper depth.

Referring to FIG. 13, according to an embodiment, the image decodingapparatus 100 may determine a second coding unit 1302 and a third codingunit 1304 of deeper depths by splitting a square first coding unit 1300based on block shape information indicating a square shape (e.g., theblock shape information may be expressed as ‘0: SQUARE’). Assuming thatthe size of the square first coding unit 1300 is 2N×2N, the secondcoding unit 1302 determined by splitting a width and height of the firstcoding unit 1300 in ½ may have a size of N×N. Furthermore, the thirdcoding unit 1304 determined by splitting a width and height of thesecond coding unit 1302 in ½ may have a size of N/2×N/2. In this case, awidth and height of the third coding unit 1304 are ¼ times those of thefirst coding unit 1300. When a depth of the first coding unit 1300 is D,a depth of the second coding unit 1302, the width and height of whichare ½ times those of the first coding unit 1300, may be D+1, and a depthof the third coding unit 1304, the width and height of which are ¼ timesthose of the first coding unit 1300, may be D+2.

According to an embodiment, the image decoding apparatus 100 maydetermine a second coding unit 1312 or 1322 and a third coding unit 1314or 1324 of deeper depths by splitting a non-square first coding unit1310 or 1320 based on block shape information indicating a non-squareshape (e.g., the block shape information may be expressed as ‘1: NS_VER’indicating a non-square shape, a height of which is longer than a width,or as ‘2: NS_HOR’ indicating a non-square shape, a width of which islonger than a height).

The image decoding apparatus 100 may determine a second coding unit1302, 1312, or 1322 by splitting at least one of a width and height ofthe first coding unit 1310 having a size of N×2N. That is, the imagedecoding apparatus 100 may determine the second coding unit 1302 havinga size of N×N or the second coding unit 1322 having a size of N×N/2 bysplitting the first coding unit 1310 in a horizontal direction, or maydetermine the second coding unit 1312 having a size of N/2×N bysplitting the first coding unit 1310 in horizontal and verticaldirections.

According to an embodiment, the image decoding apparatus 100 maydetermine the second coding unit 1302, 1312, or 1322 by splitting atleast one of a width and height of the first coding unit 1320 having asize of 2N×N. That is, the image decoding apparatus 100 may determinethe second coding unit 1302 having a size of N×N or the second codingunit 1312 having a size of N/2×N by splitting the first coding unit 1320in a vertical direction, or may determine the second coding unit 1322having a size of N×N/2 by splitting the first coding unit 1320 inhorizontal and vertical directions.

According to an embodiment, the image decoding apparatus 100 maydetermine a third coding unit 1304, 1314, or 1324 by splitting at leastone of a width and height of the second coding unit 1302 having a sizeof N×N. That is, the image decoding apparatus 100 may determine thethird coding unit 1304 having a size of N/2×N/2, the third coding unit1314 having a size of N/4×N/2, or the third coding unit 1324 having asize of N/2×N/4 by splitting the second coding unit 1302 in vertical andhorizontal directions.

According to an embodiment, the image decoding apparatus 100 maydetermine the third coding unit 1304, 1314, or 1324 by splitting atleast one of a width and height of the second coding unit 1312 having asize of N/2×N. That is, the image decoding apparatus 100 may determinethe third coding unit 1304 having a size of N/2×N/2 or the third codingunit 1324 having a size of N/2×N/4 by splitting the second coding unit1312 in a horizontal direction, or may determine the third coding unit1314 having a size of N/4×N/2 by splitting the second coding unit 1312in vertical and horizontal directions.

According to an embodiment, the image decoding apparatus 100 maydetermine the third coding unit 1304, 1314, or 1324 by splitting atleast one of a width and height of the second coding unit 1322 having asize of N×N/2. That is, the image decoding apparatus 100 may determinethe third coding unit 1304 having a size of N/2×N/2 or the third codingunit 1314 having a size of N/4×N/2 by splitting the second coding unit1322 in a vertical direction, or may determine the third coding unit1324 having a size of N/2×N/4 by splitting the second coding unit 1322in vertical and horizontal directions.

According to an embodiment, the image decoding apparatus 100 may splitthe square coding unit 1300, 1302, or 1304 in a horizontal or verticaldirection. For example, the image decoding apparatus 100 may determinethe first coding unit 1310 having a size of N×2N by splitting the firstcoding unit 1300 having a size of 2N×2N in a vertical direction, or maydetermine the first coding unit 1320 having a size of 2N×N by splittingthe first coding unit 1300 in a horizontal direction. According to anembodiment, when a depth is determined based on the length of thelongest side of a coding unit, a depth of a coding unit determined bysplitting the first coding unit 1300 having a size of 2N×2N in ahorizontal or vertical direction may be the same as the depth of thefirst coding unit 1300.

According to an embodiment, a width and height of the third coding unit1314 or 1324 may be ¼ times those of the first coding unit 1310 or 1320.When a depth of the first coding unit 1310 or 1320 is D, a depth of thesecond coding unit 1312 or 1322, the width and height of which are ½times those of the first coding unit 1310 or 1320, may be D+1, and adepth of the third coding unit 1314 or 1324, the width and height ofwhich are ¼ times those of the first coding unit 1310 or 1320, may beD+2.

FIG. 14 illustrates depths that are determinable based on shapes andsizes of coding units, and part indexes (PIDs) that are fordistinguishing the coding units, according to an embodiment.

According to an embodiment, the image decoding apparatus 100 maydetermine various-shape second coding units by splitting a square firstcoding unit 1400. Referring to FIG. 14, the image decoding apparatus 100may determine second coding units 1402 a and 1402 b, 1404 a and 1404 b,and 1406 a, 1406 b, 1406 c, and 1406 d by splitting the first codingunit 1400 in at least one of vertical and horizontal directions based onsplit shape mode information. That is, the image decoding apparatus 100may determine the second coding units 1402 a and 1402 b, 1404 a and 1404b, and 1406 a, 1406 b, 1406 c, and 1406 d, based on the split shape modeinformation of the first coding unit 1400.

According to an embodiment, depths of the second coding units 1402 a and1402 b, 1404 a and 1404 b, and 1406 a, 1406 b, 1406 c, and 1406 d thatare determined based on the split shape mode information of the squarefirst coding unit 1400 may be determined based on the length of a longside thereof. For example, because the length of a side of the squarefirst coding unit 1400 equals the length of a long side of thenon-square second coding units 1402 a and 1402 b, and 1404 a and 1404 b,the first coding unit 1400 and the non-square second coding units 1402 aand 1402 b, and 1404 a and 1404 b may have the same depth, e.g., D.However, when the image decoding apparatus 100 splits the first codingunit 1400 into the four square second coding units 1406 a, 1406 b, 1406c, and 1406 d based on the split shape mode information, because thelength of a side of the square second coding units 1406 a, 1406 b, 1406c, and 1406 d is ½ times the length of a side of the first coding unit1400, a depth of the second coding units 1406 a, 1406 b, 1406 c, and1406 d may be D+1 which is deeper than the depth D of the first codingunit 1400 by 1.

According to an embodiment, the image decoding apparatus 100 maydetermine a plurality of second coding units 1412 a and 1412 b, and 1414a, 1414 b, and 1414 c by splitting a first coding unit 1410, a height ofwhich is longer than a width, in a horizontal direction based on thesplit shape mode information. According to an embodiment, the imagedecoding apparatus 100 may determine a plurality of second coding units1422 a and 1422 b, and 1424 a, 1424 b, and 1424 c by splitting a firstcoding unit 1420, a width of which is longer than a height, in avertical direction based on the split shape mode information.

According to an embodiment, a depth of the second coding units 1412 aand 1412 b, and 1414 a, 1414 b, and 1414 c, or 1422 a and 1422 b, and1424 a, 1424 b, and 1424 c, which are determined based on the splitshape mode information of the non-square first coding unit 1410 or 1420,may be determined based on the length of a long side thereof. Forexample, because the length of a side of the square second coding units1412 a and 1412 b is ½ times the length of a long side of the firstcoding unit 1410 having a non-square shape, a height of which is longerthan a width, a depth of the square second coding units 1412 a and 1412b is D+1 which is deeper than the depth D of the non-square first codingunit 1410 by 1.

Furthermore, the image decoding apparatus 100 may split the non-squarefirst coding unit 1410 into an odd number of second coding units 1414 a,1414 b, and 1414 c based on the split shape mode information. The oddnumber of second coding units 1414 a, 1414 b, and 1414 c may include thenon-square second coding units 1414 a and 1414 c and the square secondcoding unit 1414 b. In this case, because the length of a long side ofthe non-square second coding units 1414 a and 1414 c and the length of aside of the square second coding unit 1414 b are ½ times the length of along side of the first coding unit 1410, a depth of the second codingunits 1414 a, 1414 b, and 1414 c may be D+1 which is deeper than thedepth D of the non-square first coding unit 1410 by 1. The imagedecoding apparatus 100 may determine depths of coding units split fromthe first coding unit 1420 having a non-square shape, a width of whichis longer than a height, by using the above-described method ofdetermining depths of coding units split from the first coding unit1410.

According to an embodiment, the image decoding apparatus 100 maydetermine PIDs for identifying split coding units, based on a size ratiobetween the coding units when an odd number of split coding units do nothave equal sizes. Referring to FIG. 14, a coding unit 1414 b of a centerlocation among an odd number of split coding units 1414 a, 1414 b, and1414 c may have a width equal to that of the other coding units 1414 aand 1414 c and a height which is two times that of the other codingunits 1414 a and 1414 c. That is, in this case, the coding unit 1414 bat the center location may include two of the other coding unit 1414 aor 1414 c. Therefore, when a PID of the coding unit 1414 b at the centerlocation is 1 based on a scan order, a PID of the coding unit 1414 clocated next to the coding unit 1414 b may be increased by 2 and thusmay be 3. That is, discontinuity in PID values may be present. Accordingto an embodiment, the image decoding apparatus 100 may determine whetheran odd number of split coding units do not have equal sizes, based onwhether discontinuity is present in PIDs for identifying the splitcoding units.

According to an embodiment, the image decoding apparatus 100 maydetermine whether to use a specific splitting method, based on PIDvalues for identifying a plurality of coding units determined bysplitting a current coding unit. Referring to FIG. 14, the imagedecoding apparatus 100 may determine an even number of coding units 1412a and 1412 b or an odd number of coding units 1414 a, 1414 b, and 1414 cby splitting the first coding unit 1410 having a rectangular shape, aheight of which is longer than a width. The image decoding apparatus 100may use PIDs indicating respective coding units so as to identify therespective coding units. According to an embodiment, the PID may beobtained from a sample at a preset location of each coding unit (e.g.,an upper-left sample).

According to an embodiment, the image decoding apparatus 100 maydetermine a coding unit at a preset location from among the split codingunits, by using the PIDs for distinguishing the coding units. Accordingto an embodiment, when the split shape mode information of the firstcoding unit 1410 having a rectangular shape, a height of which is longerthan a width, indicates to split a coding unit into three coding units,the image decoding apparatus 100 may split the first coding unit 1410into three coding units 1414 a, 1414 b, and 1414 c. The image decodingapparatus 100 may assign a PID to each of the three coding units 1414 a,1414 b, and 1414 c. The image decoding apparatus 100 may compare PIDs ofan odd number of split coding units to determine a coding unit at acenter location from among the coding units. The image decodingapparatus 100 may determine the coding unit 1414 b having a PIDcorresponding to a middle value among the PIDs of the coding units, asthe coding unit at the center location from among the coding unitsdetermined by splitting the first coding unit 1410. According to anembodiment, the image decoding apparatus 100 may determine PIDs fordistinguishing split coding units, based on a size ratio between thecoding units when the split coding units do not have equal sizes.Referring to FIG. 14, the coding unit 1414 b generated by splitting thefirst coding unit 1410 may have a width equal to that of the othercoding units 1414 a and 1414 c and a height which is two times that ofthe other coding units 1414 a and 1414 c. In this case, when the PID ofthe coding unit 1414 b at the center location is 1, the PID of thecoding unit 1414 c located next to the coding unit 1414 b may beincreased by 2 and thus may be 3. When the PID is not uniformlyincreased as described above, the image decoding apparatus 100 maydetermine that a coding unit is split into a plurality of coding unitsincluding a coding unit having a size different from that of the othercoding units. According to an embodiment, when the split shape modeinformation indicates to split a coding unit into an odd number ofcoding units, the image decoding apparatus 100 may split a currentcoding unit in such a manner that a coding unit of a preset locationamong an odd number of coding units (e.g., a coding unit of a centerlocation) has a size different from that of the other coding units. Inthis case, the image decoding apparatus 100 may determine the codingunit of the center location, which has a different size, by using PIDsof the coding units. However, the PIDs and the size or location of thecoding unit of the preset location are not limited to theabove-described examples, and various PIDs and various locations andsizes of coding units may be used.

According to an embodiment, the image decoding apparatus 100 may use apreset data unit where a coding unit starts to be recursively split.

FIG. 15 illustrates that a plurality of coding units are determinedbased on a plurality of preset data units included in a picture,according to an embodiment.

According to an embodiment, a preset data unit may be defined as a dataunit where a coding unit starts to be recursively split by using splitshape mode information. That is, the preset data unit may correspond toa coding unit of an uppermost depth, which is used to determine aplurality of coding units split from a current picture. In the followingdescriptions, for convenience of explanation, the preset data unit isreferred to as a reference data unit.

According to an embodiment, the reference data unit may have a presetsize and a preset shape. According to an embodiment, a reference codingunit may include M×N samples. Herein, M and N may be equal to eachother, and may be integers expressed as powers of 2. That is, thereference data unit may have a square or non-square shape, and may besplit into an integer number of coding units.

According to an embodiment, the image decoding apparatus 100 may splitthe current picture into a plurality of reference data units. Accordingto an embodiment, the image decoding apparatus 100 may split theplurality of reference data units, which are split from the currentpicture, by using the split shape mode information of each referencedata unit. The operation of splitting the reference data unit maycorrespond to a splitting operation using a quadtree structure.

According to an embodiment, the image decoding apparatus 100 maypreviously determine the minimum size allowed for the reference dataunits included in the current picture. Accordingly, the image decodingapparatus 100 may determine various reference data units having sizesequal to or greater than the minimum size, and may determine one or morecoding units by using the split shape mode information with reference tothe determined reference data unit.

Referring to FIG. 15, the image decoding apparatus 100 may use a squarereference coding unit 1500 or a non-square reference coding unit 1502.According to an embodiment, the shape and size of reference coding unitsmay be determined based on various data units capable of including oneor more reference coding units (e.g., sequences, pictures, slices, slicesegments, tiles, tile groups, largest coding units, or the like).

According to an embodiment, the receiver 110 of the image decodingapparatus 100 may obtain, from a bitstream, at least one of referencecoding unit shape information and reference coding unit size informationwith respect to each of the various data units. An operation ofsplitting the square reference coding unit 1500 into one or more codingunits has been described above in relation to the operation of splittingthe current coding unit 300 of FIG. 3, and an operation of splitting thenon-square reference coding unit 1502 into one or more coding units hasbeen described above in relation to the operation of splitting thecurrent coding unit 400 or 450 of FIG. 4. Thus, detailed descriptionsthereof will not be provided herein.

According to an embodiment, the image decoding apparatus 100 may use aPID for identifying the size and shape of reference coding units, todetermine the size and shape of reference coding units according to somedata units previously determined based on a preset condition. That is,the receiver 110 may obtain, from the bitstream, only the PID foridentifying the size and shape of reference coding units with respect toeach slice, slice segment, tile, tile group, or largest coding unitwhich is a data unit satisfying a preset condition (e.g., a data unithaving a size equal to or smaller than a slice) among the various dataunits (e.g., sequences, pictures, slices, slice segments, tiles, tilegroups, largest coding units, or the like). The image decoding apparatus100 may determine the size and shape of reference data units withrespect to each data unit, which satisfies the preset condition, byusing the PID. When the reference coding unit shape information and thereference coding unit size information are obtained and used from thebitstream according to each data unit having a relatively small size,efficiency of using the bitstream may not be high, and therefore, onlythe PID may be obtained and used instead of directly obtaining thereference coding unit shape information and the reference coding unitsize information. In this case, at least one of the size and shape ofreference coding units corresponding to the PID for identifying the sizeand shape of reference coding units may be previously determined. Thatis, the image decoding apparatus 100 may determine at least one of thesize and shape of reference coding units included in a data unit servingas a unit for obtaining the PID, by selecting the previously determinedat least one of the size and shape of reference coding units based onthe PID.

According to an embodiment, the image decoding apparatus 100 may use oneor more reference coding units included in a largest coding unit. Thatis, a largest coding unit split from a picture may include one or morereference coding units, and coding units may be determined byrecursively splitting each reference coding unit. According to anembodiment, at least one of a width and height of the largest codingunit may be integer times at least one of the width and height of thereference coding units. According to an embodiment, the size ofreference coding units may be obtained by splitting the largest codingunit n times based on a quadtree structure. That is, the image decodingapparatus 100 may determine the reference coding units by splitting thelargest coding unit n times based on a quadtree structure, and may splitthe reference coding unit based on at least one of the block shapeinformation and the split shape mode information according to variousembodiments.

FIG. 16 illustrates a processing block serving as a unit for determininga determination order of reference coding units included in a picture,according to an embodiment.

According to an embodiment, the image decoding apparatus 100 maydetermine one or more processing blocks split from a picture. Theprocessing block is a data unit including one or more reference codingunits split from a picture, and the one or more reference coding unitsincluded in the processing block may be determined according to aspecific order. That is, a determination order of one or more referencecoding units determined in each processing block may correspond to oneof various types of orders for determining reference coding units, andmay vary depending on the processing block. The determination order ofreference coding units, which is determined with respect to eachprocessing block, may be one of various orders, e.g., raster scan order,Z-scan, N-scan, up-right diagonal scan, horizontal scan, and verticalscan, but is not limited to the above-mentioned scan orders.

According to an embodiment, the image decoding apparatus 100 may obtainprocessing block size information and may determine the size of one ormore processing blocks included in the picture. The image decodingapparatus 100 may obtain the processing block size information from abitstream and may determine the size of one or more processing blocksincluded in the picture. The size of processing blocks may be a presetsize of data units, which is indicated by the processing block sizeinformation.

According to an embodiment, the receiver 110 of the image decodingapparatus 100 may obtain the processing block size information from thebitstream according to each specific data unit. For example, theprocessing block size information may be obtained from the bitstream ina data unit such as an image, sequence, picture, slice, slice segment,tile, or tile group. That is, the receiver 110 may obtain the processingblock size information from the bitstream according to each of thevarious data units, and the image decoding apparatus 100 may determinethe size of one or more processing blocks, which are split from thepicture, by using the obtained processing block size information. Thesize of the processing blocks may be integer times that of the referencecoding units.

According to an embodiment, the image decoding apparatus 100 maydetermine the size of processing blocks 1602 and 1612 included in thepicture 1600. For example, the image decoding apparatus 100 maydetermine the size of processing blocks based on the processing blocksize information obtained from the bitstream. Referring to FIG. 16,according to an embodiment, the image decoding apparatus 100 maydetermine a width of the processing blocks 1602 and 1612 to be fourtimes the width of the reference coding units, and may determine aheight of the processing blocks 1602 and 1612 to be four times theheight of the reference coding units. The image decoding apparatus 100may determine a determination order of one or more reference codingunits in one or more processing blocks.

According to an embodiment, the image decoding apparatus 100 maydetermine the processing blocks 1602 and 1612, which are included in thepicture 1600, based on the size of processing blocks, and may determinea determination order of one or more reference coding units in theprocessing blocks 1602 and 1612. According to an embodiment,determination of reference coding units may include determination of thesize of the reference coding units.

According to an embodiment, the image decoding apparatus 100 may obtain,from the bitstream, determination order information of one or morereference coding units included in one or more processing blocks, andmay determine a determination order with respect to one or morereference coding units based on the obtained determination orderinformation. The determination order information may be defined as anorder or direction for determining the reference coding units in theprocessing block. That is, the determination order of reference codingunits may be independently determined with respect to each processingblock.

According to an embodiment, the image decoding apparatus 100 may obtain,from the bitstream, the determination order information of referencecoding units according to each specific data unit. For example, thereceiver 110 may obtain the determination order information of referencecoding units from the bitstream according to each data unit such as animage, sequence, picture, slice, slice segment, tile, tile group, orprocessing block. Because the determination order information ofreference coding units indicates an order for determining referencecoding units in a processing block, the determination order informationmay be obtained with respect to each specific data unit including aninteger number of processing blocks.

According to an embodiment, the image decoding apparatus 100 maydetermine one or more reference coding units based on the determineddetermination order.

According to an embodiment, the receiver 110 may obtain thedetermination order information of reference coding units from thebitstream as information related to the processing blocks 1602 and 1612,and the image decoding apparatus 100 may determine a determination orderof one or more reference coding units included in the processing blocks1602 and 1612 and determine one or more reference coding units, whichare included in the picture 1600, based on the determination order.Referring to FIG. 16, the image decoding apparatus 100 may determinedetermination orders 1604 and 1614 of one or more reference coding unitsin the processing blocks 1602 and 1612, respectively. For example, whenthe determination order information of reference coding units isobtained with respect to each processing block, different types of thedetermination order information of reference coding units may beobtained for the processing blocks 1602 and 1612. When the determinationorder 1604 of reference coding units in the processing block 1602 is araster scan order, reference coding units included in the processingblock 1602 may be determined according to a raster scan order. On thecontrary, when the determination order 1614 of reference coding units inthe other processing block 1612 is a backward raster scan order,reference coding units included in the processing block 1612 may bedetermined according to the backward raster scan order.

According to an embodiment, the image decoding apparatus 100 may decodethe determined one or more reference coding units. The image decodingapparatus 100 may decode an image, based on the reference coding unitsdetermined as described above. A method of decoding the reference codingunits may include various image decoding methods.

According to an embodiment, the image decoding apparatus 100 may obtainblock shape information indicating the shape of a current coding unit orsplit shape mode information indicating a splitting method of thecurrent coding unit, from the bitstream, and may use the obtainedinformation. The split shape mode information may be included in thebitstream related to various data units. For example, the image decodingapparatus 100 may use the split shape mode information included in asequence parameter set, a picture parameter set, a video parameter set,a slice header, a slice segment header, a tile header, or a tile groupheader. Furthermore, the image decoding apparatus 100 may obtain, fromthe bitstream, a syntax element corresponding to the block shapeinformation or the split shape mode information according to eachlargest coding unit, each reference coding unit, or each processingblock, and may use the obtained syntax element.

Hereinafter, a method of determining a split rule, according to anembodiment of the disclosure will be described in detail.

The image decoding apparatus 100 may determine a split rule of an image.The split rule may be predetermined between the image decoding apparatus100 and the image encoding apparatus 2200. The image decoding apparatus100 may determine the split rule of the image, based on informationobtained from a bitstream. The image decoding apparatus 100 maydetermine the split rule based on the information obtained from at leastone of a sequence parameter set, a picture parameter set, a videoparameter set, a slice header, a slice segment header, a tile header,and a tile group header. The image decoding apparatus 100 may determinethe split rule differently according to frames, slices, tiles, temporallayers, largest coding units, or coding units.

The image decoding apparatus 100 may determine the split rule based on ablock shape of a coding unit. The block shape may include a size, shape,a ratio of width and height, and a direction of the coding unit. Theimage encoding apparatus 2200 and the image decoding apparatus 100 maypre-determine to determine the split rule based on the block shape ofthe coding unit. However, the embodiment is not limited thereto. Theimage decoding apparatus 100 may determine the split rule based on theinformation obtained from the bitstream received from the image encodingapparatus 2200.

The shape of the coding unit may include a square and a non-square. Whenthe lengths of the width and height of the coding unit are the same, theimage decoding apparatus 100 may determine the shape of the coding unitto be a square. Also, when the lengths of the width and height of thecoding unit are not the same, the image decoding apparatus 100 maydetermine the shape of the coding unit to be a non-square.

The size of the coding unit may include various sizes, such as 4×4, 8×4,4×8, 8×8, 16×4, 16×8, and to 256×256. The size of the coding unit may beclassified based on the length of a long side of the coding unit, thelength of a short side, or the area. The image decoding apparatus 100may apply the same split rule to coding units classified as the samegroup. For example, the image decoding apparatus 100 may classify codingunits having the same lengths of the long sides as having the same size.Also, the image decoding apparatus 100 may apply the same split rule tocoding units having the same lengths of long sides.

The ratio of the width and height of the coding unit may include 1:2,2:1, 1:4, 4:1, 1:8, 8:1, 1:16, 16:1, 32:1, 1:32, or the like. Also, adirection of the coding unit may include a horizontal direction and avertical direction. The horizontal direction may indicate a case inwhich the length of the width of the coding unit is longer than thelength of the height thereof. The vertical direction may indicate a casein which the length of the width of the coding unit is shorter than thelength of the height thereof.

The image decoding apparatus 100 may adaptively determine the split rulebased on the size of the coding unit. The image decoding apparatus 100may differently determine an allowable split shape mode based on thesize of the coding unit. For example, the image decoding apparatus 100may determine whether splitting is allowed based on the size of thecoding unit. The image decoding apparatus 100 may determine a splitdirection according to the size of the coding unit. The image decodingapparatus 100 may determine an allowable split type according to thesize of the coding unit.

The split rule determined based on the size of the coding unit may be asplit rule predetermined between the image encoding apparatus 2200 andthe image decoding apparatus 100. Also, the image decoding apparatus 100may determine the split rule based on the information obtained from thebitstream.

The image decoding apparatus 100 may adaptively determine the split rulebased on a location of the coding unit. The image decoding apparatus 100may adaptively determine the split rule based on the location of thecoding unit in the image.

Also, the image decoding apparatus 100 may determine the split rule suchthat coding units generated via different splitting paths do not havethe same block shape. However, an embodiment is not limited thereto, andthe coding units generated via different splitting paths have the sameblock shape. The coding units generated via the different splittingpaths may have different decoding processing orders. Because thedecoding processing orders have been described above with reference toFIG. 12, details thereof are not provided again.

Hereinafter, a video encoding or decoding method and apparatus will bedescribed in detail with reference to FIGS. 17 to 20, according to anembodiment of the disclosure, in which whether a current block is incontact with an upper boundary of a largest coding unit including thecurrent block is determined, when it is determined that the currentblock is in contact with the upper boundary of the largest coding unit,an upper reference line of the current block is determined as onereference line, when it is determined that the current block is not incontact with the upper boundary of the largest coding unit, the upperreference line of the current block is determined based on N referencelines, and prediction on the current block is performed based on thedetermined upper reference line.

FIG. 17 illustrates a block diagram of a video encoding apparatusaccording to an embodiment.

A video encoding apparatus 1700 according to an embodiment may include amemory 1710 and at least one processor 1720 connected to the memory1710. The operations of the video encoding apparatus 1700 according tothe embodiment may be performed as individual processors or may beperformed under the control of a central processor. Also, the memory1710 of the video encoding apparatus 1700 may store data received fromthe outside, data generated by a processor, for example, informationabout an upper reference line of a current block, etc.

The processor 1720 of the video encoding apparatus 1700 may beconfigured to determine whether a current block is in contact with anupper boundary of a largest coding unit including the current block,when it is determined that the current block is in contact with theupper boundary of the largest coding unit, determine an upper referenceline of the current block as one reference line, when it is determinedthat the current block is not in contact with the upper boundary of thelargest coding unit, determine the upper reference line of the currentblock based on N reference lines, and based on the determined upperreference line, perform prediction on the current block.

Hereinafter, specific operations of a video encoding method will bedescribed in detail with reference to FIG. 18, in which the videoencoding apparatus 1700 according to the embodiment is configured todetermine whether a current block is in contact with an upper boundaryof a largest coding unit including the current block, when it isdetermined that the current block is in contact with the upper boundaryof the largest coding unit, determine an upper reference line of thecurrent block as one reference line, when it is determined that thecurrent block is not in contact with the upper boundary of the largestcoding unit, determine the upper reference line of the current blockbased on N reference lines, and based on the determined upper referenceline, perform prediction on the current block.

FIG. 18 illustrates a flowchart of a video encoding method according toan embodiment.

Referring to FIG. 18, in operation S1810, the video encoding apparatus1700 may determine whether a current block is in contact with an upperboundary of a largest coding unit including the current block.

In operation S1830, when it is determined that the current block is incontact with the upper boundary of the largest coding unit, the videoencoding apparatus 1700 may determine an upper reference line of thecurrent block as one reference line.

According to an embodiment, the one reference line may be a referenceline in contact with the upper side of the current block.

In operation S1850, when it is determined that the current block is notin contact with the upper boundary of the largest coding unit, the videoencoding apparatus 1700 may determine the upper reference line of thecurrent block based on N reference lines. Here, N is a natural number.

According to an embodiment, the video encoding apparatus 1700 maygenerate reference line information indicating a value of N.

According to an embodiment, when it is determined that the current blockis in contact with the upper boundary of the largest coding unit, thereference line information may not be generated.

According to an embodiment, the value of N is determined throughcalculation of sum of transform difference (SATD) or rate distortionoptimization (RDO), and thus the reference line information indicating Nmay be encoded.

According to an embodiment, when it is determined that the current blockis not in contact with the upper boundary of the largest coding unit andN is 1, the upper reference line may be determined as a first referenceline in contact with the upper side of the current block.

According to an embodiment, when it is determined that the current blockis not in contact with the upper boundary of the largest coding unit andN is 2, the upper reference line may include the first reference line incontact with the upper side of the current block and a second referenceline in contact with the upper side of the first reference line.

According to another embodiment, when it is determined that the currentblock is not in contact with the upper boundary of the largest codingunit and N is 2, the upper reference line may be determined as thesecond reference line in contact with the upper side of the firstreference line in contact with the upper side of the current block. Thatis, when N is 2, a reference line located second on the upper side ofthe current block may be determined as the upper reference line.

According to an embodiment, when it is determined that the current blockis not in contact with the upper boundary of the largest coding unit andN is 3, the upper reference line may include the first reference line incontact with the upper side of the current block, the second referenceline in contact with the upper side of the first reference line, and afourth reference line in contact with the upper side of a thirdreference line in contact with the upper side of the second referenceline.

According to another embodiment, when it is determined that the currentblock is not in contact with the upper boundary of the largest codingunit and N is 3, the upper reference line may be determined as thefourth reference line in contact with the upper side of the thirdreference line in contact with the upper side of the second referenceline in contact with the upper side of the first reference line incontact with the upper side of the current block. That is, when N is 3,a reference line located fourth on the upper side of the current blockmay be determined as the upper reference line.

According to an embodiment, a left reference line located on the leftside of the current block may be determined based on N reference lineslocated on the left side of the current block.

In operation S1870, the video encoding apparatus 1700 may performprediction on the current block based on the determined upper referenceline.

According to an embodiment, prediction on the current block may beperformed by using the determined upper reference line and the leftreference line determined based on the N reference lines located on theleft side of the current block.

FIGS. 19 and 20 are a block diagram of a video decoding apparatusaccording to an embodiment and a flowchart of a video decoding methodaccording to an embodiment, which correspond to the video encodingapparatus and the video encoding method described above, respectively.

FIG. 19 illustrates a block diagram of a video decoding apparatusaccording to an embodiment.

A video decoding apparatus 1900 according to an embodiment may include amemory 1910 and at least one processor 1920 connected to the memory1910. The operations of the video decoding apparatus 1900 according tothe embodiment may be performed as individual processors or may beperformed under the control of a central processor. Also, the memory1910 of the video decoding apparatus 1900 may store data received fromthe outside, data generated by a processor, for example, informationabout an upper reference line of a current block, etc.

The processor 1920 of the video decoding apparatus 1900 may beconfigured to determine whether a current block is in contact with anupper boundary of a largest coding unit including the current block,when it is determined that the current block is in contact with theupper boundary of the largest coding unit, determine an upper referenceline of the current block as one reference line, when it is determinedthat the current block is not in contact with the upper boundary of thelargest coding unit, determine the upper reference line of the currentblock based on N reference lines, and based on the determined upperreference line, perform prediction on the current block.

Hereinafter, specific operations of a video encoding method will bedescribed in detail with reference to FIG. 20, in which the videodecoding apparatus 1900 according to the embodiment is configured todetermine whether a current block is in contact with an upper boundaryof a largest coding unit including the current block, when it isdetermined that the current block is in contact with the upper boundaryof the largest coding unit, determine an upper reference line of thecurrent block as one reference line, when it is determined that thecurrent block is not in contact with the upper boundary of the largestcoding unit, determine the upper reference line of the current blockbased on N reference lines, and based on the determined upper referenceline, perform prediction on the current block.

FIG. 20 illustrates a flowchart of a video decoding method according toan embodiment.

Referring to FIG. 20, in operation S2010, the video decoding apparatus1900 may determine whether a current block is in contact with an upperboundary of a largest coding unit including the current block.

In operation S2030, when it is determined that the current block is incontact with the upper boundary of the largest coding unit, the videodecoding apparatus 1900 may determine an upper reference line of thecurrent block as one reference line.

In operation S2050, when it is determined that the current block is notin contact with the upper boundary of the largest coding unit, the videodecoding apparatus 1900 may determine the upper reference line of thecurrent block based on N reference lines.

According to an embodiment, N may be determined by reference lineinformation obtained from a bitstream.

According to an embodiment, when it is determined that the current blockis in contact with the upper boundary of the largest coding unit, thereference line information may not be obtained.

According to an embodiment, when it is determined that the current blockis not in contact with the upper boundary of the largest coding unit andN is 1, the upper reference line may be determined as a first referenceline in contact with the upper side of the current block.

According to an embodiment, when it is determined that the current blockis not in contact with the upper boundary of the largest coding unit andN is 2, the upper reference line may include the first reference line incontact with the upper side of the current block and a second referenceline in contact with the upper side of the first reference line.

According to another embodiment, when it is determined that the currentblock is not in contact with the upper boundary of the largest codingunit and N is 2, the upper reference line may be determined as thesecond reference line in contact with the upper side of the firstreference line in contact with the upper side of the current block. Thatis, when N is 2, a reference line located second on the upper side ofthe current block may be determined as the upper reference line.

According to an embodiment, when it is determined that the current blockis not in contact with the upper boundary of the largest coding unit andN is 3, the upper reference line may include the first reference line incontact with the upper side of the current block, the second referenceline in contact with the upper side of the first reference line, and afourth reference line in contact with the upper side of a thirdreference line in contact with the upper side of the second referenceline.

According to another embodiment, when it is determined that the currentblock is not in contact with the upper boundary of the largest codingunit and N is 3, the upper reference line may be determined as thefourth reference line in contact with the upper side of the thirdreference line in contact with the upper side of the second referenceline in contact with the upper side of the first reference line incontact with the upper side of the current block. That is, when N is 3,a reference line located fourth on the upper side of the current blockmay be determined as the upper reference line.

According to an embodiment, a left reference line located on the leftside of the current block may be determined based on N reference lineslocated on the left side of the current block.

In operation S2070, the video decoding apparatus 1900 may performprediction on the current block based on the determined upper referenceline.

According to an embodiment, prediction on the current block may beperformed by using the determined upper reference line and the leftreference line determined based on the N reference lines located on theleft side of the current block.

According to an embodiment, when a reference sample having no samplevalue exists in the upper reference line, the reference sample having nosample value in the upper reference line may be padded by using apredetermined default value. That is, a sample value of the referencesample having no sample value in the upper reference line may bedetermined as the predetermined default value.

According to an embodiment, when the reference sample having no samplevalue exists in the upper reference line, a reference sample having nosample value in the upper reference line may be padded with a value ofthe reference sample having a sample value in the upper reference line.That is, a sample value of the reference sample having no sample valuein the upper reference line may be determined as the value of thereference sample having a sample value in the upper reference line.

According to an embodiment, when the reference sample having no samplevalue exists in the upper reference line, the reference sample having nosample value in the upper reference line may be regenerated by using thevalue of the reference sample having a sample value in the upperreference line.

According to an embodiment, when a reference line having no sample valueexists in the upper reference line, a sample value of the reference linehaving no sample value may be padded by using a predetermined defaultvalue. That is, the sample value of the reference line having no samplevalue may be determined as the predetermined default value.

According to an embodiment, when the reference line having no samplevalue exists in the upper reference line, the reference sample having nosample value may be padded with the value of the reference sample havinga sample value. That is, the sample value of the reference line havingno sample value may be determined as a sample value of the referenceline having a sample value.

According to an embodiment, when the reference line having no samplevalue exists in the upper reference line, a sample of the reference linehaving no sample value may be regenerated by using the sample value ofthe reference line having a sample value.

When the current block is in contact with the upper boundary of thelargest coding unit including the current block, by using one referenceline, the problem of an increase in the size of a reference line buffercaused by using a plurality of reference lines may be solved. In detail,in a case where the plurality of reference lines are stored in thereference line buffer and used, when the current block is in contactwith the upper boundary of the largest coding unit including the currentblock, only one reference line closest to the upper boundary is stored,and thus the size of the buffer may be reduced in terms of the largestcoding unit. For example, even though prediction is performed by usingonly one reference line among a plurality of reference lines, in orderto determine which line of the plurality of reference lines to be used,all of the plurality of reference lines are required to be stored.However, when the current block is in contact with the upper boundary,only one reference line in contact with the upper boundary is stored andused, and thus the size of the buffer is reduced in terms of the largestcoding unit.

According to an embodiment, a method will be described below withreference to FIG. 21, in which, when the current block is in contactwith the upper boundary of the largest coding unit including the currentblock, one upper reference line is used, and when the current block isnot in contact with the upper boundary of the largest coding unit, areference line is determined based on N upper reference lines.

FIG. 21 is a diagram for describing a method of using at least onereference line, according to an embodiment.

Referring to FIG. 21, in a case of multi reference line prediction usingat least one reference line, reference lines 2121, 2131, 2141, and 2151located on the upper side of a current block 2110 and reference line2122, 2132, 2142, and 2152 located on the left side of the current block2110 may be used. In detail, the reference lines located on the upperside may include a first upper reference line 2121 in contact with theupper side of the current block 2110, a second upper reference line 2131in contact with the upper side of the first upper reference line 2121, athird upper reference line 2141 in contact with the upper side of thesecond upper reference line 2131, and a fourth upper reference line 2151in contact with the upper side of the third upper reference line 2141.The reference lines located on the left side may include a first leftreference line 2122 in contact with the left side of the current block2110, a second left reference line 2132 in contact with the left side ofthe first left reference line 2122, a third left reference line 2142 incontact with the left side of the second left reference line 2132, and afourth left reference line 2152 in contact with the left side of thethird left reference line 2142.

Also, in the multi reference line prediction, the third upper referenceline 2141 and the third left reference line 2142 may not be used. Indetail, because the most efficient reference sample is used for themulti reference line prediction by identifying samples at variouslocations, a third reference line may not be used and at least one offirst, second, and fourth reference lines may be used.

In the following embodiments related to FIG. 21, it is described thatthe number of reference lines available for each of the upper and theleft sides of a current block is N. In this case, “available” does notmean whether a reference line exists, but the possibility that thereference line is used in an algorithm used for prediction.

Hereinafter, in the specification, “MRL index” is an index indicatingone reference line used for prediction of the current block among aplurality of reference lines used in the multi reference lineprediction.

According to an embodiment, when N is 1 (MRL index=0), in prediction onthe current block 2110, the first upper reference line 2121 in contactwith the upper side of the current block 2110 and first left referenceline 2122 in contact with the left side of the current block 2110 may beused. That is, when “MRL index” is 0, the first upper reference line2121 and the left reference line, which are first reference lines of theupper reference lines and the left reference lines of the current block2110, may be used.

According to an embodiment, when N is 2, in prediction on the currentblock 2110, the first upper reference line 2121 in contact with theupper side of the current block 2110, the second upper reference line2131 in contact with the upper side of the first upper reference line2121, the first left reference line 2122 in contact with the left sideof the current block 2110, and the second left reference line 2132 incontact with the left side of the first left reference line 2122 may beused.

According to another embodiment, when N is 1 (MRL index=1), inprediction on the current block 2110, the second upper reference line2131 on the upper side of the current block 2110 and second leftreference line 2132 on the left side of the current block 2110 may beused. That is, when “MRL index” is 1, the second upper reference line2131 and the second left reference line 2132, which are second referencelines of the upper reference lines and the left reference lines of thecurrent block 2110, may be used.

According to an embodiment, when N is 3, in prediction on the currentblock 2110, the first upper reference line 2121 in contact with theupper side of the current block 2110, the second upper reference line2131 in contact with the upper side of the first upper reference line2121, the fourth upper reference line 2151 in contact with the upperside of the third upper reference line 2141 in contact with the upperside of the second upper reference line 2131, the first left referenceline 2122 in contact with the left side of the current block 2110, thesecond left reference line 2132 in contact with the left side of thefirst left reference line 2122, and the fourth left reference line 2152in contact with the left side of the third left reference line 2142 incontact with the left side of the second left reference line 2132 may beused. That is, three upper reference lines that are the first upperreference line 2121, the second upper reference line 2131, and thefourth upper reference line 2151 and three left reference lines that arethe first left reference line 2122, the second left reference line 2132,and the fourth left reference line 2152 may be used.

According to another embodiment, when N is 3 (MRL index=2), inprediction on the current block 2110, the fourth upper reference line2151 on the upper side of the current block 2110 and fourth leftreference line 2152 on the left side of the current block 2110 may beused. That is, when “MRL index” is 2, the fourth upper reference line2151 and the fourth left reference line 2152, which are fourth referencelines of the upper reference lines and the left reference lines of thecurrent block 2110, may be used.

According to an embodiment, when the current block 2110 is in contactwith the upper boundary of the largest coding unit including the currentblock 2110 and N is 1 (MRL index=0), in prediction on the current block2110, the first upper reference line 2121 on the upper side of thecurrent block 2110 and the first left reference line 2122 on the leftside of the current block 2110 may be used.

According to an embodiment, when the current block 2110 is in contactwith the upper boundary of the largest coding unit including the currentblock 2110 and N is 2, in prediction on the current block 2110, thefirst upper reference line 2121 on the upper side of the current block2110, and the first left reference line 2122 and the second leftreference line 2132 on the left side of the current block 2110 may beused.

According to another embodiment, when the current block 2110 is incontact with the upper boundary of the largest coding unit including thecurrent block 2110 and N is 2 (MRL index=1), in prediction on thecurrent block 2110, the first upper reference line 2121 on the upperside of the current block 2110 and the second left reference line 2132on the left side of the current block 2110 may be used. According to anembodiment, when the current block 2110 is in contact with the upperboundary of the largest coding unit including the current block 2110 andN is 3, in prediction on the current block 2110, the first upperreference line 2121 on the upper side of the current block 2110, and thefirst left reference line 2122, the second left reference line 2132, andthe fourth left reference line 2152 on the left side of the currentblock 2110 may be used.

According to another embodiment, when the current block 2110 is incontact with the upper boundary of the largest coding unit including thecurrent block 2110 and N is 3 (MRL index=2), in prediction on thecurrent block 2110, the first upper reference line 2121 on the upperside of the current block 2110 and the fourth left reference line 2152on the left side of the current block 2110 may be used.

According to an embodiment, at the encoding side, N is determinedthrough SATD or RDO calculation, and thus reference line informationindicating N may be signaled.

According to an embodiment, at the encoding side, when the current block2110 is in contact with the upper boundary of the largest coding unitincluding the current block 2110, the reference line informationindicating N may not be generated.

According to an embodiment, at the decoding side, N may be determinedthrough the signaled reference line information indicating N.

According to an embodiment, at the decoding side, when the current block2110 is in contact with the upper boundary of the largest coding unitincluding the current block 2110, the reference line informationindicating N may not be obtained.

FIG. 22 illustrates a flowchart of a video encoding method according toanother embodiment.

The video encoding apparatus 1700 of FIG. 17 may perform operationsaccording to the video encoding method of FIG. 22.

The video encoding apparatus 1700 may include the memory 1710 and the atleast one processor 1720 connected to the memory 1710. The operations ofthe video encoding apparatus 1700 according to the embodiment may beperformed as individual processors or may be performed under the controlof a central processor. Also, the memory 1710 of the video encodingapparatus 1700 may store data received from the outside, data generatedby a processor, for example, information about an upper reference lineof a current luma block, etc.

The processor 1720 of the video encoding apparatus 1700 may beconfigured to determine whether a current luma block is in contact withan upper boundary of a largest coding unit including the current lumablock, when it is determined that the current luma block is in contactwith the upper boundary of the largest coding unit, determine an upperreference line of the current luma block as one reference line, when itis determined that the current luma block is not in contact with theupper boundary of the largest coding unit, determine the upper referenceline of the current luma block as two reference lines, and based on thedetermined upper reference line, perform prediction on a current chromablock corresponding to the current luma block.

Referring to FIG. 22, in operation S2210, the video encoding apparatus1700 may determine whether the current luma block is in contact with theupper boundary of the largest coding unit including the current lumablock.

In operation S2230, when it is determined that the current luma block isin contact with the upper boundary of the largest coding unit, the videoencoding apparatus 1700 may determine an upper reference line of thecurrent luma block as one reference line.

In operation S2250, when it is determined that the current luma block isnot in contact with the upper boundary of the largest coding unit, thevideo encoding apparatus 1700 may determine the upper reference line ofthe current luma block as two reference lines.

According to an embodiment, the two upper reference lines may include afirst reference line in contact with the upper side of the current lumablock and a second reference line in contact with the upper side of thefirst reference line.

In operation S2270, the video encoding apparatus 1700 may performprediction on a current chroma block corresponding to the current lumablock based on the determined upper reference line.

According to an embodiment, prediction may be performed on the currentchroma block corresponding to the current luma block, based on thedetermined upper reference line and two left reference lines.

According to an embodiment, weight information and deviation informationare determined by using a relationship between luma reference samples ofthe current luma block included in the upper reference line and a chromareference sample in contact with the upper side of the current chromablock, and the current chroma block is determined based on the weightinformation, the deviation information, and luma samples of the currentluma block so that prediction may be performed on the current chromablock.

FIG. 23 illustrates a flowchart of a video decoding method according toanother embodiment.

A video decoding apparatus 1900 of FIG. 19 may perform operationsaccording to the video encoding method of FIG. 23.

The video decoding apparatus 1900 may include the memory 1910 and the atleast one processor 1920 connected to the memory 1910. The videodecoding apparatus 1900 according to the embodiment may operate asindividual processors or may be operated under the control of a centralprocessor. Also, the memory 1910 of the video decoding apparatus 1900may store data received from the outside, data generated by a processor,for example, information about an upper reference line of a current lumablock, etc.

The processor 1920 of the video decoding apparatus 1900 may beconfigured to determine whether a current luma block is in contact withan upper boundary of a largest coding unit including the current lumablock, when it is determined that the current luma block is in contactwith the upper boundary of the largest coding unit, determine an upperreference line of the current luma block as one reference line, when itis determined that the current luma block is not in contact with theupper boundary of the largest coding unit, determine the upper referenceline of the current luma block as two reference lines, and based on thedetermined upper reference line, perform prediction on a current chromablock corresponding to the current luma block.

Referring to FIG. 23, in operation S2310, the video decoding apparatus1900 may determine whether the current luma block is in contact with theupper boundary of the largest coding unit including the current lumablock.

In operation S2330, when it is determined that the current luma block isin contact with the upper boundary of the largest coding unit, the videodecoding apparatus 1900 may determine an upper reference line of thecurrent luma block as one reference line.

In operation S2350, when it is determined that the current luma block isnot in contact with the upper boundary of the largest coding unit, thevideo decoding apparatus 1900 may determine the upper reference line ofthe current luma block as two reference lines.

According to an embodiment, the two upper reference lines may include afirst reference line in contact with the upper side of the current lumablock and a second reference line in contact with the upper side of thefirst reference line.

In operation S2370, the video decoding apparatus 1900 may performprediction on a current chroma block corresponding to the current lumablock based on the determined upper reference line.

According to an embodiment, prediction may be performed on the currentchroma block corresponding to the current luma block, based on thedetermined upper reference line and two left reference lines.

According to an embodiment, weight information and deviation informationare determined by using a relationship between luma reference samples ofthe current luma block included in the upper reference line and a chromareference sample in contact with the upper side of the current chromablock, and the current chroma block is determined based on the weightinformation, the deviation information, and luma samples of the currentluma block so that prediction may be performed on the current chromablock.

A method of performing prediction on a current chroma block by using arelationship between a luma reference sample of a current luma block anda chroma reference sample of the current chroma block will be describedbelow with reference to FIGS. 24A to 25B.

FIG. 24A illustrates luma samples located around a current luma blockand a chroma sample located around a current chroma block, according toan embodiment, and FIG. 24B illustrates luma samples of a current lumablock and a chroma sample of a current chroma block, according to anembodiment.

Referring to FIGS. 24A and 24B, weight information and deviationinformation about a correlation between 6 luma samples L₁ to L₆ 2450among reconstructed adjacent luma samples 2430 neighboring a currentluma block 2470 in a luma block 2410 and a chroma sample 2460 ofreconstructed adjacent chroma samples 2440 neighboring a current chromablock 2480 in a chroma block 2420 may be derived, and by using theweight information, the deviation information, and reconstructed lumasamples L₁ to L₆ 2490 of the current luma block 2470, derived by amethod expressed by Equation 1, a chroma sample ĉ 2491 of the currentchroma block 2480 may be reconstructed.

According to an embodiment, one or more chroma samples may be predictedby using N predetermined luma samples to predict a chroma sample. Also,the N predetermined luma samples may be a luma sample of a current lumablock corresponding to a location of a chroma sample of a current chromablock and adjacent samples of the luma sample of the correspondingcurrent luma block, or may be the luma sample of the current luma blockcorresponding to the location of the chroma sample of the current chromablock and arbitrary samples not neighboring the luma sample of thecorresponding current luma block.

More specifically, a predictor ĉ of the chroma sample may be expressedby Equation 1 or 2.

{circumflex over (C)}=ω₁ ΔL ₁ +ω ₂ ΔL ₂ +ω ₃ ΔL ₃ +ω ₄ ΔL ₄ +ω ₅ ΔL ₅ +ω₆ ΔL ₆+μ  [Equation 1]

{circumflex over (C)}=ω₁ L ₁+ω₂ L ₂+ω₃ L ₃+ω₄ L ₄+ω₅ L ₅+ω₆ L₆+μ  [Equation 2]

As seen in Equations 1 and 2, the predictor ĉ of the chroma sample mayrepresent a value obtained by adding a deviation to a weighted sum ofsample values (for example, L₁) of luma samples or differences (e.g.,ΔL₁) that are differences between the luma samples and an average valueof the luma samples and weights (e.g., ω₁) corresponding to therespective samples values or the respective differences.

According to an embodiment, some of weights ω₁ to ω_(N) may be zero.

According to an embodiment, a prediction mode of an adjacent luma blockof a current chroma block may be an intra prediction mode, weightinformation may be a modeling parameter value representing a correlationbetween a luma sample of the adjacent luma block and a chroma sample ofan adjacent chroma block, and a chroma sample of a current chroma blockmay be reconstructed by using 6 luma samples among reconstructed lumasamples of the current luma block, 6 weights respectively correspondingto the 6 luma samples, and a deviation value of deviation information,wherein the 6 weights may be a value obtained by multiplying a fixedweight determined in advance according to the intra prediction mode bythe modeling parameter value representing the correlation between theluma sample and the chroma sample.

When Ip represents the intra prediction mode, the modeling parametersω₁, . . . , ω_(N) may be replaced by s·ω′_(ip,1), . . . , s·ω′_(ip,N),respectively, and according to the intra prediction mode, the modelingparameters s·ω′_(ip,1), . . . , s·ω′_(ip,N) may use only modelingparameters s and p by fixing a value of ω′_(ip,1), . . . , ω′_(ip,N).

According to an embodiment, the weights ω′_(ip,1), . . . , ω′_(ip,N)fixed according to the intra prediction mode may have the same value inthe form of a Gaussian filter, etc. regardless of the intra predictionmode, or have different values according to the intra prediction mode.

FIG. 25A illustrates luma samples located around a current luma blockand a chroma sample located around a current chroma block, according toanother embodiment, and FIG. 25B illustrates luma samples of a currentluma block and a chroma sample of a current chroma block, according toanother embodiment.

Referring to FIGS. 25A and 25B, when a current luma block is in contactwith an upper boundary of a largest coding unit including the currentluma block, one reference line in contact with the upper side of thecurrent luma block is used.

In detail, weight information and deviation information about acorrelation between 3 luma samples L′₁ to L′₃ 2550 included in onereference line in contact with the upper side of a current luma block2570 among reconstructed adjacent luma samples 2530 neighboring thecurrent luma block 2570 in a luma block 2510 and a chroma sample 2560 ofreconstructed adjacent chroma samples 2540 neighboring a current chromablock 2580 in a chroma block 2520 may be derived, and by using theweight information, the deviation information, and reconstructed lumasamples L′₁ to L′₃ 2590 of the current luma block 2570, derived by amethod expressed by Equation 1, a chroma sample ĉ 2591 of the currentchroma block 2580 may be reconstructed.

Also, because two reference lines are used as a reference line incontact with the left side of the current luma block, as seen in FIGS.24A and 24B, weight information and deviation information about acorrelation between 6 adjacent luma samples and an adjacent chromasample are derived, and by using the reconstructed luma samples L₁ to L62490 of the current luma block 2470, the chroma sample ĉ 2491 of thecurrent chroma block 2480 may be reconstructed.

According to an embodiment, when the current luma block is in contactwith the upper boundary of the largest coding unit including the currentluma block, the number and locations of samples to be used to predict achroma block from a luma block under a condition of using one referenceline in contact with the upper side of the current luma block may bechanged according to an algorithm.

Also, even when the current luma block is not in contact with the upperboundary of the largest coding unit including the current luma block,the number and locations of the samples to be used to predict the chromablock from the luma block may be changed according to the algorithm.

FIG. 26A illustrates an embodiment in which the number of upperreference lines is different from the number of left reference lines,FIG. 26B illustrates an embodiment in which the number of upperreference lines is the same as the number of left reference lines, andFIG. 26C illustrates an embodiment in which, when the number of upperreference lines is different from the number of left reference lines,padding is performed so that the number of upper reference lines and thenumber of left reference line are the same.

Referring to FIG. 26A, according to an embodiment, the number of anupper reference line 2620 of a current block 2610 may be different fromthe number of a left reference line 2630 of the current block 2610. Indetail, the number of the upper reference line 2620 located on the upperside of the current block 2610 is determined as N, and the number of theleft reference line 2630 located on the left side of the current block2610 is determined as M, wherein M may be greater than or equal to N. Nmay be determined as a value of a maximum line buffer set in the codec.For example it may be N=2 and M=4, N=1 and M=2, or N=1 and M=4.

According to an embodiment, referring to FIG. 26A, when the currentblock 2610 is in contact with an upper boundary of a largest coding unitincluding the current block 2610, the number of the upper reference line2620 located on the upper side of the current block 2610 is determinedas N, and the number of the left reference line 2630 located on the leftside of the current block 2610 is determined as M, wherein M may begreater than or equal to N. N may be determined as a value of a maximumline buffer set in the codec. For example it may be N=2 and M=4, N=1 andM=2, or N=1 and M=4.

According to an embodiment, when a current block is in contact with anupper boundary of a largest coding unit including the current block,whether one reference line or use N predetermined reference lines are tobe used may be determined through a flag. Whether the one reference lineor use the N predetermined reference lines are to be used may bedetermined through a flag in a frame unit, a largest coding unit, or ablock unit.

According to another embodiment, when the current block is in contactwith the upper boundary of the largest coding unit including the currentblock, whether one reference line or N predetermined reference lines areto be used by a decoding apparatus may be determined without a separateflag, depending on the availability of a reference block of the currentblock.

When the current block is in contact with the upper boundary of thelargest coding unit including the current block, in a case where a flagindicating whether one reference line or N predetermined reference linesare to be used, the flag may be simultaneously applied to both a lumablock and a chroma block, or may be individually applied to a luma blockand a chroma block. Also, when the current block is in contact with theupper boundary of the largest coding unit including the current block,whether one reference line or N predetermined reference lines are to beused may be determined according to different criteria (e.g., a blocksize, an intra mode, reference availability) for each of the luma blockand the chroma block.

According to another embodiment, when the current block is in contactwith the upper boundary of the largest coding unit including the currentblock, whether one reference line or N predetermined reference lines areto be used may be determined according to a size of the current blockwithout signaling of the flag.

According to an embodiment, through a flag of a tool (e.g., LM chroma,adaptive loop filter (ALF), etc.) using a plurality of reference lines,whether a plurality of reference lines are to be used when the currentblock is in contact with the upper boundary of the largest coding unitincluding the current block may be determined.

According to an embodiment, by obtaining flag information of the tool inadvance for each largest coding unit, only in a case where a rate of theflag being turned on is N % or higher, when the current block is incontact with the upper boundary of the largest coding unit including thecurrent block, it may be permissible to use the plurality of referencelines.

According to an embodiment, by determining whether a tool of an adjacentlargest coding unit of the largest coding unit including the currentblock is turned on/off, in a case where a rate of a flag of the adjacentlargest coding unit being turned on is M % (e.g., M is 50) or higher,when the current block is in contact with the upper boundary of thelargest coding unit including the current block, it may be permissibleto use the plurality of reference lines. In detail, all of largestcoding units available as adjacent largest coding units may be used, orinformation about whether tools of only some largest coding units areturned on may be selectively used. Also, not all of the adjacent largestcoding units are used, and only information about whether a tool of acoding unit adjacent to the largest coding unit including the currentblock is turned on/off may be used.

According to an embodiment, by using information about surroundings,whether the flag is to be applied may be determined without separatesignaling.

Also, referring to FIG. 26B, when a current block 2611 is not in contactwith the upper boundary of the largest coding unit, both the number ofan upper reference line 2621 of the current block 2611 and the number ofa left reference line 2631 of the current block 2611 may be determinedas M.

Referring to FIG. 26C, when the number of an upper reference line 2622of a current block 2612 is N and the number of a left reference line2632 of the current block 2612 is M, in a case where the number of upperreference lines and the number of left reference lines are required tobe the same, an area equal to M−N above the N upper reference lines 2622may be filled by padding the area with upper pixels of the N upperreference lines 2622.

In this case, pixels of the area equal to M−N may be generated by usingpixels of one or more reference lines in the N upper reference lines2622. At this time, various methods such as padding, extrapolation,filtering, etc. may be used as generation methods.

According to an embodiment, when the number of the N upper referencelines 2622 is two or more, the area equal to M−N above the N upperreference line 2622 may be filled by padding the area with a gradientbetween to two adjacent reference lines.

When the current block 2612 is in contact with the upper boundary of thelargest coding unit including the current block 2612, in a case only oneupper line is used, a method of using a tool changes according toconditions, and thus, as in the embodiment described above, as manyreference lines as originally required may be generated through padding,linear extrapolation, or non-linear filtering using one upper line. Inthis case, other surrounding information that may be used may be usedtogether.

The disclosure has been particularly shown and described with referenceto embodiments thereof. In this regard, it will be understood by one ofordinary skill in the art that various changes in form and details maybe made therein without departing from the scope of the disclosure.Therefore, the embodiments should be considered in a descriptive senseonly and not for purposes of limitation. The scope of the disclosure isdefined not by the detailed descriptions of the disclosure but by thefollowing claims, and all differences within the scope will be construedas being included in the disclosure.

Meanwhile, the aforedescribed embodiments of the disclosure may bewritten as a program executable on a computer, and may be implemented ingeneral-use digital computers that execute the program by using acomputer-readable recording medium. Examples of the computer-readablerecording medium include magnetic storage media (e.g., ROM, floppydisks, hard disks, etc.), optical recording media (e.g., CD-ROMs, orDVDs), or the like.

1. A video decoding method comprising: determining whether a currentblock is in contact with an upper boundary of a largest coding unitincluding the current block; when it is determined that the currentblock is in contact with the upper boundary of the largest coding unit,determining an upper reference line of the current block as onereference line; when it is determined that the current block is not incontact with the upper boundary of the largest coding unit, determiningthe upper reference line of the current block based on N referencelines; and performing prediction on the current block, based on thedetermined upper reference line, wherein N is a natural number.
 2. Thevideo decoding method of claim 1, wherein N is determined according toreference line information obtained from a bitstream.
 3. The videodecoding method of claim 2, wherein, when it is determined that thecurrent block is in contact with the upper boundary of the largestcoding unit, the reference line information is not obtained.
 4. Thevideo decoding method of claim 1, wherein, when N is 2, the upperreference line is determined as a second reference line in contact withan upper side of a first reference line in contact with an upper side ofthe current block.
 5. The video decoding method of claim 1, wherein,when N is 3, the upper reference line is determined as a fourthreference line in contact with an upper side of a third reference linein contact with an upper side of a second reference line in contact withan upper side of a first reference line in contact with an upper side ofthe current block.
 6. The video decoding method of claim 1, wherein aleft reference line located in a left side of the current block isdetermined based on the N reference lines.
 7. The video decoding methodof claim 1, wherein, when a reference line having no sample value existsin the upper reference line, a sample value of the reference line havingno sample value is padded with a predetermined default value.
 8. Thevideo decoding method of claim 1, wherein, when a reference line havingno sample value exists in the upper reference line, a reference samplehaving no sample value is padded with a value of a reference samplehaving a sample value, or a sample of the reference line having nosample value is regenerated by using a sample value of a reference linehaving a sample value.
 9. A video decoding method comprising:determining whether a current luma block is in contact with an upperboundary of a largest coding unit including the current luma block; whenit is determined that the current luma block is in contact with theupper boundary of the largest coding unit, determining an upperreference line of the current luma block as one reference line; when itis determined that the current luma block is not in contact with theupper boundary of the largest coding unit, determining the upperreference line of the current luma block as two reference lines; andperforming prediction on a current chroma block corresponding to thecurrent luma block, based on the determined upper reference line. 10.The video decoding method of claim 9, wherein the two reference linescomprise a first reference line in contact with an upper side of thecurrent luma block and a second reference line in contact with an upperside of the first reference line.
 11. The video decoding method of claim9, wherein weight information and deviation information are determinedbased on a relationship between luma reference samples of the currentluma block included in the upper reference line and a chroma referencesample in contact with an upper side of the current chroma block, and bydetermining the current chroma block based on the weight information,the deviation information, and luma samples of the current luma block,prediction is performed on the current chroma block.
 12. A videoencoding method comprising: determining whether a current block is incontact with an upper boundary of a largest coding unit including thecurrent block; when it is determined that the current block is incontact with the upper boundary of the largest coding unit, determiningan upper reference line of the current block as one reference line; whenit is determined that the current block is not in contact with the upperboundary of the largest coding unit, determining the upper referenceline of the current block based on N reference lines; and performingprediction on the current block, based on the determined upper referenceline, wherein N is a natural number.
 13. The video encoding method ofclaim 12, further comprising generating reference line informationindicating a value of N.
 14. The video encoding method of claim 13,wherein, when it is determined that the current block is in contact withthe upper boundary of the largest coding unit, the reference lineinformation is not generated.
 15. The video encoding method of claim 11,wherein, when N is 3, the upper reference line is determined as a fourthreference line in contact with an upper side of a third reference linein contact with an upper side of a second reference line in contact withan upper side of a first reference line in contact with an upper side ofthe current block.